Introduction: Partial Knee Replacement (PKR) is an appealing alternative to Total Knee Replacement (TKR) when the patient has isolated compartment osteoarthritis (OA). In nearly all cases there is a radiolucency observed between the tibial tray wall and the boney interface. The reasons why radiolucencies appear are unknown, but the bone will adapt to its altered mechanical environment by bone remodelling in accordance with ‘Wollf’s Law’. The aim of this study was to investigate the mechanical environment of the tibia bone adjacent to the tray wall, following cemented and cementless PKR, in order to determine whether this region of bone resorbs.

Methods: A validated finite element (FE) model of a cadaver tibia implanted with an Oxford PKR was used in this study. Kinematic data from fluoroscopy measurements during a step-up activity were used to determine the relative tibio-femoral positioning for the Oxford PKR model. Load data were adapted from the in-vivo measured loads using an instrumented implant during a step-up activity. The standard operating protocol was simulated for the Oxford PKR FE models, with the tibial tray implanted in a neutral position. The tibia was sectioned around the tray. Zone 7 was defined as parallel to the vertical tray wall, corresponding to the region on screened x-rays where radiolucencies are observed. It was assumed that the bone in the implanted tibia will attempt to normalise its stress-strain patterns locally to its equilibrium state, the intact tibia, for the same loading conditions. Forty patients (20 cemented, 20 cementless) who had undergone PKR were randomly selected from a database, and their screened x-rays assessed for radiolucency in region 7.

Results: The SED in region 7 was 80% lower in the cemented and cementless tibia, compared to the intact tibia (Figure 2). The maximum tensile stress was 63% lower in the cemented and cementless tibia, compared to the intact tibia. The corresponding maximum compressive stress was 52% lower. Radiolucency was observed in all forty radiographs in region 7.

Discussion: After implantation with a cemented or cementless PKR the bone strains and SED in region 7 are reduced. This reduction may provide the signal for adaptive bone remodelling and bone will be resorbed from this region, decreasing the volume and increasing the SED. Bone resorption will continue until the equilibrium state is reached. If a ‘lazy’ zone between 35% and 50% of the remodelling signal is considered, bone resorption will still occur due to the large decrease in SED for this region. For region 7 to return its SED to the equilibrium state, its volume will need to be reduced by 80%. This is likely to be the reason why a radiolucency is observed clinically in this region in almost every case, whether a cemented or cementless implant is used.

The results of mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing (five-year survival: 82%). Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to a high dislocation rate. A detailed analysis confirmed the elevated lateral tibial joint line to be a contributory factor to bearing dislocation. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications included use of a domed tibial component.

The aim of this study is to compare the outcome of these iterations: the original series (series I), those with improved surgical technique (series II) and the domed tibial component (series III). The primary outcome measure was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In the original series (n=53), implanted using a standard open approach, there were six dislocations in the first year, the average flexion 110°, and 95% had no/mild pain on activity. In the second series (n=65), there were 3 dislocations, the average flexion was 117°, and 80% had no/mild pain on activity.

In the third series with the modified technique and a convex domed tibial plateau, there was one dislocation, average flexion was 125° and 94% had no/mild pain on activity. At four years the cumulative primary dislocation rates were 10%, 5% and 0% respectively, and were significantly different (p=0.04).

The improved surgical technique and implant design has reduced dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR.

About ten years ago we introduced sophisticated instrumentation and an increased range of component sizes for the Oxford unicompartmental knee replacement (UKR) to facilitate a minimally invasive surgical (MIS) approach. The device is now routinely implanted through an incision from the medial pole of the patella to the tibial tuberosity. This has resulted in a more rapid recovery and an improved functional result. As the access to the knee is limited there is a concern that the long term results may be compromised. The aim of this study was to determine the 10 year survival.

A prospective follow up of all Phase 3 minimally invasive Oxford UKR implanted by two senior authors (DWM & CAFD) has been undertaken. So far 1015 UKRs have been implanted for anteromedial osteoarthritis. All patients received a cemented implant through a MIS approach and were followed up prospectively by an independent observer. The data was collected prospectively regarding pre-operative status, complications and clinical as well as functional outcome at predetermined intervals.

The average age of patients was 66.4 years (range: 33 – 88) with mean Oxford Knee Score 41 (SD: 7.9) at the time of last follow up, Knee Society Score (objective) of 84 (SD: 13) and Knee Society Score (functional) of 83 (SD: 21). At ten years the survival of this cohort is 96%. There were 22 revisions including 7 for progression of arthritis, 5 for infection, 5 for bearing dislocation, 4 for unexplained pain and one for rupture of ACL secondary to trauma.

We conclude that the Oxford Knee can be implanted reliably through a minimally invasive approach, giving excellent long term results.

Introduction: This study explores whether modern magnetic resonance imaging (MRI) with improved cartilage sequencing is able to show a more detailed view of antero-medial osteoarthritis of the knee (AMOA) than previously, so enabling a radiographic description of this common phenotype of disease. Modern MRI technology allows us to visualize in great detail the structures and cartilage within the knee, providing a better understanding of the pathoanatomy of AMOA. This description of the end stage of disease is useful as a baseline when investigating the progression of arthritis through the knee. Preoperative assessment of patients and selection of intervention is very important and preoperative imaging forms an integral part of this. This will also be useful in preoperative assessment and surgical management of patients.

Methods: 50 patients with a radiographic diagnosis of anteromedial osteoarthritis of the knee and had been listed for unicompartmental knee arthroplasty (UKA) had MRI as part of their pre-op workup. At operation all were deemed suitable for UKA using the current Oxford indications. The image sequences were coronal, axial and sagittal with a predetermined cartilage protocol. The state of the ACL, cartilage wear degree and location, presence and pattern of osteophytes, meniscal anatomy and subchondral high signal were assessed.

Results: All the ACLs were visualized and in continuity, however 40% showed intrasubstance high signal. 100% of medial compartments showed full thickness anteromedial loss with preservation of the posteromedial cartilage. When present, the meniscus was extruded in 75% of cases.

90% of lateral compartments were normal and none had full thickness cartilage loss. However 10% showed high signal in the tibial plateau. There was a highly reproducible pattern of osteophyte formation; 94% posteromedial and posterolateral aspect of medial femoral condyle; 90% medial tibial; 80% medial femoral and 84% lateral intercondylar notch.

Discussion: This study maps the pattern of anteromedial osteoarthritis using modern MRI techniques. This creates a baseline description of disease which is useful when investigating disease progression. This also has importance in determining preoperative indications (preservation of ACL and posteromedial cartilage); surgical technique (determine pattern of osteophytes requiring resection) and potentially important for long-term outcome (early lateral compartment changes).

Patello-femoral instability (PFI) affects 40 individuals per 100,000 population and causes significant morbidity. The causes of patello-femoral instability are multi-factorial, and an isolated anatomical abnormality does not necessarily indicate instability. Patello-femoral subluxation ranges from 0% (stable patella tracking) to 100% (dislocation) and there is an established relationship between the amount of subluxation and anterior knee pain. Traditionally, magnetic resonance (MR) imaging and standard radiographs are used to guide the clinician towards a suitable corrective procedure for PFI. The multi-factorial nature of patello-femoral instability is not addressed with current imaging techniques. This study aims to address which anatomical variables assessed on MR images are most relevant to patello-femoral subluxation. This information will aid surgical decision making, particularly in selecting the most appropriate reconstructive surgery.

A retrospective analysis of MR studies of 60 patients with suspected patello-femoral instability was performed. All patients were graded for degree of subluxation using a dynamic MR scan.

The patient scans were assessed for the presence of a specific range of anatomical variables:

patella alta, (modified Insall-Salvatti)

The Wilk’s Lambda test for multi-variate analysis was used to establish whether any relationship was present between the degree of patello-femoral instability and bony or soft tissue anatomical variables. Non-parametric statistical tests were applied across the groups and within the groups to assess their relative significance.

The following variables showed a significant relationship with patellofemoral subluxation; distance of the VMO from the patella (< 0.001), TTD (< 0.001), patella engagement (0.001), sulcus angles (0.004) and patella alta (0.005).

This study agrees with previous work showing a significant correlation between subluxation and trochlea sulcus angle and TTD.

This is the first study to establish a significant correlation between patella engagement and radiological instability. The lower the percentage engagement of the patella in the trochlea, the greater the degree of patello-femoral instability. Patella engagement showed a more significant relationship with subluxation than patella alta.

We report a new method of predicting patello-femoral instability by measuring the overlap of the patella in the trochlea groove.

Introduction: Most unicompartmental knee replacements (UKRs) employ cement for fixation of the prosthetic components to the bone. The information in the literature about the relative merits of cemented and cementless UKR is contradictory, with some favouring cementless fixation while others favouring cemented fixation. There is concern about the radiolucency which frequently develops around the tibial component with cemented fixations. The exact cause of the occurrence of radiolucency is unknown but according to some, it may suggest suboptimal fixation.

Method: Following ethical approval, 62 patients with medial OA were randomised to receive either cemented (n=31) or cementless components (n=31). All patients underwent identical surgical procedure with either a cemented or cementless Oxford UKR. Patients were assessed clinically and radiologically. The x-rays were taken with an image intensifier (I.I.). The position of the I.I. was adjusted until it was perfectly aligned with the tibial bone-implant interface thereby allowing accurate assessment of presence and extent of the radiolucency.

Results: The patients in the two groups were well matched. There was no significant difference in the clinical scores between the two groups. The mean OKS for the cemented group was 40 (± 8.3) and 42 (± 4.6) for cementless group. Narrow radiolucent lines were seen at the bone-implant interfaces of 75% of the cemented tibial components; partial in 43% and complete in 32%. In the cementless implants, partial radiolucencies were seen in 7% and complete radiolucencies in none. The differences are statistically highly significant (p< 0.0001) and imply satisfactory bone ingrowth into the cementless implants.

Conclusions: The method of fixation influences the incidence of radiolucency. With identical designs, no patient with cementless components developed any complete radiolucency. The observation raises the question as to whether cementless rather than cemented components should be routinely used for UKR.

Purpose: The purpose of this study was to report the mid-term survival results of Oxford UKAs in patients of 50 years of age or less, using (1) revision surgery and (2) Oxford Knee Scores (OKS) as outcome measures.

Method: A literature review identified studies of Oxford mobile bearing UKAs containing individuals 1) 50 years old or less with 2) medial osteoarthritis and 3) 2 years or longer follow-up. Authors were approached to participate in a multi-centre survival analysis by submitting all their patients, 50 years of age or less, who received a medial UKA for osteoarthritis. Patients who had died, been lost to follow-up or who underwent revision were identified. OKS were established for all patients with surviving implants.

Results: Seven centres submitted 107 patients. The mean age was 47 years (range 32–50). The average follow-up was 4 years (range 1–25). Forty-seven patients had follow-up into their fifth year or longer. The cumulative 7-year survival using revision as the endpoint was 96% (CI 8). The mean post-operative OKS for surviving implants was 38 (CI 2) out of a possible 48.

Conclusion: While early survival rates and function are encouraging, long-term follow-up is required before concluding UKA is a viable treatment option in young patients with unicompartmental knee arthritis.

Introduction: This study explores whether modern magnetic resonance imaging (MRI) with improved cartilage sequencing is able to show a more detailed view of anteromedial osteoarthritis of the knee (AMOA). Preoperative assessment of patients and selection of intervention is very important and preoperative imaging forms an integral part of this. Modern MRI technology may allow us to visualize in great detail the structures and cartilage within the knee, providing a better understanding of the pathoanatomy of AMOA. This will be useful in preoperative assessment and surgical management of patients.

Methods: 50 patients with a radiographic diagnosis of anteromedial osteoarthritis of the knee and had been listed for unicompartmental knee arthroplasty (UKA) had MRI as part of their pre-op workup. At operation all were deemed suitable for UKA using the current Oxford indications. The image sequences were coronal, axial and sagittal with a predetermined cartilage protocol. The state of the ACL, cartilage wear location and pattern, presence of osteophytes and subchondral high signal were assessed.

Results: All the ACLs were visualized and in continuity, however 40% showed intrasubstance high signal.

100% of medial compartments showed full thickness anteromedial loss with preservation of the posteromedial cartilage. When present, the meniscus was extruded in 96% of cases.

Discussion: This study maps the pattern of anteromedial osteoarthritis using modern MRI techniques. This has importance in determining preoperative indications (preservation of ACL and posteromedial cartilage); surgical technique (determine pattern of osteophytes requiring resection) and potentially important for long-term outcome (early lateral compartment changes).

Introduction: Radiolucent lines (RLL) underneath the tibial component are common findings following the Oxford Uni-compartmental Knee Arthroplasty (OUKA)[1]. Many theories have been proposed to explain the cause of RLL, such as poor cementing, osteonecrosis, micromotion, and thermal necrosis, however, the true aetiology and clinical significance remain unclear. We undertook a retrospective study analysing the association between RLL and pre-operative, intra-operative factors, as well as clinical outcome scores.

Method: One hundred and sixty-one knees which had undergone primary Phase 3 medial Oxford OUKA were included in the study. Fluoroscopic radiography films were assessed at five years post-operatively for areas of tibial RLL. The presence of RLL was compared to

patients’ pre-operative demographics for age, weight, height, BMI,

Results: Of the 161 knees in the study, 126 (78%) were found to have tibial RLL. No statistical difference was found between knees with RLL and those without in terms of preoperative demographics, intra-operative factors, or clinical assessment criteria.

Discussion: No clear relationship between RLL, preoperative demographics, and intra-operative factors has been identified in this study. We conclude that tibial RLL following OUKA is a common finding but do not seem to affect medium term clinical outcome.

Statement of purpose: Finite element (FE) models of bone can be used to evaluate new and modified knee replacements. Validation of FE models is seldom used, and the quantification of modelling parameters has a considerable effect on the results obtained. The aim of this study is to develop a FE model of a cadaveric tibia and validate it against a comprehensive set of experiments.

Summary of Methods: Seventeen tri-axial rosettes were attached to a cleaned, fresh frozen cadaveric human tibia and the tibia was subjected to 13 loading conditions. Deflection and strain data were used for comparison with the FE model. A geometric model was created on the basis of computed tomography (CT) scans. The CT data was used to map 600 orthotropic material properties to the tibia. All experiments were simulated on the FE model. Measured principal strains were compared to their corresponding FE values using regression analysis. The validated tibia model was reduced in size (75mm to the proximal) and then re-modelled to represent only the proximal tibia. This re-modelled tibia was validated against the reduced size FE model. Virtual surgery was performed on the validated proximal model to implant a UKR.

Summary of Results: For the whole tibia model, the regression line for all axial loads combined had a slope of 0.999, an intercept of −6.24 micro-strain, and an R2 value of 0.962. The root mean square error as a percentage was 5%. For the proximal tibia model, correlation coefficients of 0.989 and 0.976 were obtained for the maximum and minimum principal strains respectively.

Statement of Conclusions: An FE model of an implanted proximal tibia has been validated against experimental data. This model is able to accurately predict the deflection and stresses in a replaced knee joint to obtain clinically relevant information. This will provide a virtual model of unicompartmental arthroplasty, where variables such as fixation method and bearing mechanics can be assessed.

Introduction: The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component.

Aim: The aim of this study is to compare the outcome of these iterations: the original series [series I], Series II with improved surgical technique and the domed tibial component [Series III].

Method: The primary assessment of outcome was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In series I, there were 53 knees, in series II 65 knees and in series III 60 knees, all with a minimum of one year follow up.

Results: In series I, there were 6 bearing dislocations (11%) and the average range of movement (ROM) was 110°. In the second series, there were 2 dislocations (3%) and the average ROM was 118°. In the third series, there were no primary dislocations and the average ROM was 125°.

Conclusions: The improved surgical technique and implant design has reduced the dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR.

Purpose: To compare the site of lesions in medial and lateral unicompartmental osteoarthritis (OA) of the knee.

Methods: Patients with medial (n=35) and lateral (n=15) OA, having unicompartmental knee arthroplasty, were recruited. Intra-operatively, the distance between the anterior, posterior, medial and lateral margins of the full-thickness lesion and reference lines dividing the condyles was measured. The midpoints of lesions were calculated and groups were compared. Lateral radiographs were used to determine the relationship between the lesion site and knee flexion angle (KFA).

Results: Femoral lesion: In lateral OA, the midpoint of lesions was 25.0mm (SD:8.8) posterior to the reference line passing transversely through the apex of the inter-condylar notch. This was significantly different (p< 0.001) from midpoint in medial OA, which was 10.7mm (SD:9.4) posterior to the reference line.

Tibial lesion: In lateral OA, the midpoint of lesions was 2.0mm (SD:6.5) posterior to the reference line passing through the mid-coronal plane of the resected tibia. This was located significantly more posterior (p=0.038) than midpoint in medial OA, which was 2.2mm (SD:5.7) anterior to the reference line.

Knee Flexion Angle: In lateral OA, the midpoint of lesions was on average at 40° flexion and sites of smaller lesions were very variable. The lesion expanded both anteriorly and posteriorly. In medial OA, smaller femoral lesions occurred in full extension and extended further posteriorly with disease progression.

No significant difference was demonstrated in medial and lateral localisation of the lesions.

Conclusion: Medial OA begins near full extension, progresses in a predictable manner and is perhaps initiated by events occurring at heel strike. Lateral OA begins in flexion in a less predictable manner, at KFA above that seen during the gait cycle. The different sites of lesions in medial and lateral OA suggest different aetiology and pathophysiology. Therefore, prevention and treatment strategies should be different.

The purpose of this study was to determine if a single physiotherapy intervention would enable patients to kneel following Unicompartmental knee arthroplasty (UKA).

Kneeling is an important functional activity that is frequently not performed after knee arthroplasty, thus affecting a patient’s ability to carry out basic tasks of everyday life. There is however no clinical reason why patients should not kneel and many with proposed knee surgery ask about the possibility of kneeling after their operation.

Sixty adults participated in a prospective randomised controlled trial with blinded assessments. At 6 weeks post-operatively UKA patients were randomised to either the Routine care group where no advice on kneeling was given or to the Kneeling intervention group where participants were taught and given advice on how to kneel and were encouraged to do so. They were re-assessed at 1 year. The primary outcome measure was Question 7 of the Oxford Knee Score which asks the question “Could you kneel down and get up again afterwards?”

Pre-operatively there was no difference in the kneeling ability of the two groups. At 1 year the difference in kneeling ability between the two groups was highly significant (p< 0.05). Spearman’s correlation coefficient showed no significant association between a change in score of Question 7 at 1 year and the following factors; scar position, numbness, range of flexion, arthritic involvement of other joints and pain. Linear regression analysis also confirmed that these factors were not successful in predicting a change in kneeling ability.

This study showed that the single factor predictive of kneeling ability was the physiotherapy intervention provided at 6 weeks post-operatively and it is suggested that kneeling should be incorporated into patient’s post-operative rehabilitation programmes.

Introduction: Treatment options for the young active patient with isolated symptomatic medial compartment OA and pre-existing ACL deficiency are limited. Implant longevity and activity levels may preclude TKA, whilst HTO and unicompartmentasl knee arythroplasty (UKA) are unreliable due to ligamentous instability. UKAs tend to fail because of wear or tibial loosening resulting from eccentric loading. Combined UKA and ACL reconstruction may therefore be a solution.

Method: Fifteen patients with combined ACL reconstruction and Oxford UKA (ACLR group), were matched (age, gender and follow-up period) with 15 patients with Oxford UKA with intact ACL (ACLI group). Prospectively collected clinical and x-ray data from the last follow-up (minimum 3 years, range: 3 – 5) were compared. Ten patients from each group also underwent in-vivo kinematic assessment using a standardised protocol.

Results: At the last follow-up, the clinical outcome for the two groups were similar. One ACLR patient needed revision due to infection. Radiological assessment did not show any significant difference between relative component positions and none of the patients had pathological radiolucencies suggestive of component loosening. Kinematic assessment showed posterior placement of the femur on tibia in extension for the ACLR group, which corrected with further flexion.

Conclusions: The short-term clinical results of combined ACL reconstruction and UKA are excellent. Lack of pathological radiolucencies and near normal knee kinematics suggest that early tibial loosening due to eccentric loading is unlikely.

Aim: The aim of this study was to asses the accuracy of skyline radiographs in the assessment of the patellofemoral joint, when compared to open intraoperative assessment.

Methods: Eighty nine patients undergoing knee replacement surgery were included in the study. Skyline radiographs were obtained preoperatively. These radiographs were assessed and graded by an experienced musculoskeletal radiologist using the Altman and Ahlbäck classifications. The grades were calculated for both the medial and lateral facets of the PFJ. Intraoperative assessment of the Patellofemoral joint was undertaken at the time of surgery. The damage was graded using the modified Collins classification (0: Normal, 1: Superficial damage, 2: Partial thickness cartilage loss, 3: Focal Full thickness cartilage loss < 2cm2, 4: Extensive full thickness cartilage loss < 2cm2). Data was obtained for the Medial Facet, Lateral Facet and Trochlea.

Results: Spearman’s rank correlation coefficient between the radiographic and macroscopic changes within the lateral PFJ were poor with both the Altman 0.22 (p=0.0350) and Ahlbäck 0.24 (p=0.018). The correlation of the medial PFJ was slightly better with a coefficient for Altman 0.42 (P< 0.0001) and Ahlbäck 0.34 (P> 0.001).

Conclusion: In conclusion skyline radiographs provide a poor to moderate preoperative assessment of the degree of osteoarthritis within the patella-femoral joint. This has significant implications for establishing radiographic criteria for planning patella-femoral joint replacement.

Purpose: The aim of this study is to compare the long-term survival results of TKA in patients under the age of 60, using

revision surgery and

Method: From our knee database we identified a cohort of 60 total knee replacements that had been performed over 15 years previously. We identified those who had died, those who had been revised and established the Oxford Knee Score (OKS) for all those still surviving.

Results Using the following endpoint criteria the cumulative 15-year survival was (A) revision surgery alone = 78% (CI 12), (B) revision surgery or an OKS less than or equal to 24 (50% of total OKS) = 63% (CI 13), and (C) revision surgery or moderate pain = 48% (CI 14).

Conclusion The functional survival of TKA in patients under the age of 60 decreases in the second decade following implantation with a significant number of prostheses failing the patient due to knee pain

Introduction: The information in the literature about the relative merits of cemented and cementless unicompartmental knee replacement (UKR) is contradictory, with some favouring cementless fixation while others favouring cemented fixation. Cemented fixations give good survivorship but there is concern about the radiolucency which frequently develops around the tibial component. The exact cause of the occurrence of radiolucency is unknown but according to some, it may suggest suboptimal fixation.

Method: Sixty-two knees (31 in each group) were randomised to receive either cemented or cementless UKR components. The components were similar except that the cementless had a porous titanium and hydroxyappatite (HA) coating. Patients were prospectively assessed by an independent observer pre-operatively and annually thereafter. The clinical assessment included Oxford Knee Score, Knee Society Scores and Tegner activity score. Fluoroscopically aligned radiographs were assessed for thickness and extent of radiolucency under the tibial implant.

Results: At one year there were no differences in the clinical outcome between the groups and there were no loose components. No radiolucencies thicker than 1mm were seen. At one year none of the cementless tibias and 30% of the cemented tibias had complete radiolucencies. One out of 31 cementless (3%) and 12 out of 31 cemented (39%) had partial radiolucencies. This difference between these two groups was high significant (p< 0 0001).

Conclusions: This study clearly demonstrates that the incidence of radiolucency beneath the tibial component is influenced by component design and method of fixation. With identical designs of tibial component none of the cementless components developed complete radiolucences whereas 30% of the cemented components did. We conclude that HA achieves better bone integration than cement.

Introduction: Treatment options for the young active patient with isolated symptomatic medial compartment osteoarthritis and pre-existing anterior cruciate ligament (ACL) deficiency are limited. Implant longevity and activity levels may preclude total knee arthroplasty (TKA), whilst high tibial osteotomy HTO and unicompartmental arthroplasty (UKA) are unreliable due to ligamentous instability. UKA’s tend to fail because of wear or tibial loosening resulting from eccentric loading. Combined UKA and ACL reconstruction may therefore be a solution.

Method: Fifteen patients with combined ACL reconstruction and Oxford UKA (ACLR group), were matched (age, gender and follow-up period) with 15 patients with Oxford UKA with intact ACL (ACLI group). Prospectively collected clinical and x-ray data from the last follow-up (minimum 3 years, range: 3–5) were compared. Ten patients from each group also underwent in-vivo kinematic assessment using a standardised protocol.

Results: At the last follow-up, the clinical outcome for the two groups were similar (ACLR: OKS 46, KSS (objective): 99, ACLI: OKS 43, KSS (objective): 94). One ACLR patient needed revision due to infection. Radiological assessment did not show any significant difference between relative component positions and none of the patients had pathological radiolucencies suggestive of component loosening. Kinematic assessment showed posterior placement of the femur on tibia in extension for the ACLR group, which corrected with further flexion.

Conclusions: The short-term clinical results of combined ACL reconstruction and UKA are excellent. Lack of pathological radiolucencies and near normal knee kinematics suggest that early tibial loosening due to eccentric loading is unlikely. Similarly, wear is unlikely to be a problem because of the wear resistance of mobile bearing devices.

Introduction: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range and increased medial compartment pain than seen with its medial counterpart due to, in part, the inadequacy of a flat tibial tray replacing the domed anatomy of the lateral tibia. A new design incorporating a domed tibial component and a biconcave meniscal bearing has been developed to overcome these problems.

This study reports a clinical comparison of new and old establishing whether this modified implant has maintained the established normal kinematic profile of the Oxford UKR.

Method: Patients undergoing lateral UKR for OA were recruited for the study. Fifty one patients who underwent UKR with the domed design were compared to 60 patients who had lateral UKR with a flat inferior bearing surface. Kinematic evaluation was performed on 3 equal subgroups (n = 20); Group 1-Normal volunteer knees, Group 2-Flat Oxford Lateral UKR’s and Group 3-Domed Oxford Lateral UKR’s. The sagittal plane kinematics of each knee was assessed using videofluoroscopic analysis whilst performing a step up and deep knee bend activity. The fluoroscopic images were recorded digitally, corrected for distortion using a global correction method and analysed using specially developed software to identify the anatomical landmarks needed to determine the Patella Tendon Angle (PTA) (the angle the patella tendon and the tibial axis).

Knee kinematics were assessed by analysing the movement of the femur relative to the tibia using the PTA.

Results: PTA/KFA values, for both devices, from extension to flexion did not show any significant difference in PTA values in comparison to the normals as measured by a 3-way ANOVA. The Domed implant achieved higher maximal active flexion during the lunge exercise than those with a flat implant. Only 33% of the flat UKR’s achieved KFA of 130° or more under load whilst performing a lunge, compared with 75% of domed UKR’s and 90% of normal knees. No flat UKR achieved a KFA of 140° or more, yet 50% of all domed UKR’s did, as did 60% of all normal knees.

Conclusions: There was no significant difference in sagittal plane kinematics of the domed and flat Oxford UKR’s. Both designs had favorable kinematic profiles closely resembling that of the normal knee, suggesting normal function of the cruciate mechanism. The domed knees had a greater range of motion under load compared to the flats, approaching levels seen with the normal knee, suggesting that limited flexion for the flat plateau results from over tightening in high flexion and that this is corrected with the domed plateau. Problems with the second generation of lateral Oxford UKA have been rectified by a new bi-concave bearing without losing bearing stability and normal kinematics.

Anteromedial osteoarthritis is a distinct phenotype of osteoarthritis. The arthritic lesion on the tibia is localised to the anteromedial quadrant with an intact ACL. Deficiency of the ACL leads to a progression to tricompartmental disease. Within the spectrum of intact ACL a varying degree of ligament damage is seen. Our aim was to correlate the progression of ACL damage to the geographical extent of disease and the degree of cartilage loss on the tibial plateau.

We systematically digitally mapped 50 tibial plateau resection specimens from clinical photographs of patients undergoing unicompartmental arthroplasty, additionally the damage to their ACL was graded (0: normal, 1:synovium loss, 2:longitudinal splits)

These images were imported into image analysis software. Accurate measurements were made of the dimensions of the specimen. Measurements included the AP distance to the anterior and posterior aspect of the lesion, and the distance to the start of the macroscopically non damaged cartilage. The areas of cartilage damage and full thickness loss were also recorded. The results were represented as a % of total area to account for variation in size of the resection specimens. We compared % of full thickness loss in patients with normal to those with damaged, but functionally intact ligaments.

All specimens had a similar macroscopic appearance. A significant difference was seen with the progression of ACL damage and area of eburnation of bone. Using an unpaired t test, a significant difference in area of % full thickness cartilage loss (P=0.047) was seen between patients with a normal and longitudinal splits within their ACL. No correlation between the clinical status of the ACL and start or finish point of cartilage loss on the tibial plateau

We surmise that the progression from anteromedial to tricompartmental osteoarthritis of the knee may be related to the graduated damage of the ACL.