Introduction: Avascular necrosis of the femoral head after resurfacing hip replacement is an important complication which may lead to fracture or failure. We compared the changes in femoral head oxygenation resulting from the anterolateral approach to those resulting from the posterior approach.

Methods: In 22 patients undergoing hip resurfacing surgery, a calibrated gas-sensitive electrode was inserted supero-laterally in the femoral head via the femoral neck following division of the fascia lata. Inter-operative X-ray confirmed correct electrode placement. Baseline oxygen concentration levels were recorded immediately after electrode insertion. All results were expressed relative to this baseline, which was considered as 100% relative oxygen concentration. Oxygen levels were monitored continuously throughout the operation. 10 patients underwent surgery through the posterior approach, 12 patients through the antero-lateral approach.

Results: During the operation patterns were similar for both groups, except following joint relocation and soft tissue reconstruction; oxygen concentration recovered significantly in the anterolateral group only. The posterior approach resulted in significantly lower (p< 0.01) oxygen concentration at the end of the procedure (22%, SD 31) than the antero-lateral approach (123%, SD 99).

Discussion and Conclusion: The anterolateral approach disrupts the femoral head blood supply significantly less than the posterior approach in patients undergoing resurfacing. The incidence of complications related to avascular necrosis might be decreased by adopting blood supply conserving surgical approaches.

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.

Introduction: Interest in hip resurfacing has recently been renewed by the introduction of metal-on-metal designs; it is being increasingly used for young patients, with over 30,000 implanted worldwide. The 5 year clinical results appear promising, but there are no long term data available. Radiostereometry (RSA) measures of implant migration have been able to predict implant failure; specifically large and continuous migration predicts aseptic loosening. We present the results of a five year RSA study examining the migration of the Birmingham Hip Resurfacing (BHR).

Methods: Twenty-four subjects with primary OA were implanted with the BHR device and with bone markers for RSA. RSA measurements were taken at 3, 6, 12, 24 and 60 months. The migration of the head and the tip of femoral component were measured in 3D.

Results: Preliminary analysis showed that the total 3D migration of the head and tip over five years was 0.32mm and 0.23mm respectively.

Discussion: A distal migration of more than 0.4mm over 2 years increases the likelihood of failure in conventional stems. The total migration of the BHR was approximately 0.3mm over a five year period, significantly less than cemented THR devices. The device is stable and this is promising for long-term survival.

Background: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range, increased medial compartment pain and a higher dislocation rate than seen with its medial counterpart due to 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 current study was designed to establish whether this modi-fied ‘domed’ implant has maintained the established normal kinematic profile of the Oxford UKR.

Methods: The study population consisted of 60 participants from three equal groups; Group 1- Normal volunteer knees (n = 20), Group 2 – Flat Oxford Lateral UKR’s (n = 20) and Group 3 – Domed Oxford Lateral UKR’s (n = 20). The sagittal plane kinematics of each involved knee was assessed continuously using videofluoroscopic analysis. A standardised protocol of step-up and deep lunge was used to assess loadbearing range of motion during which the patella tendon angle (PTA) was measured as a function of the knee flexion angle (KFA).

Results: PTA/KFA values compared at 10 degree KFA increments from maximal extension to maximal flexion for all 3 groups did not demonstrate any statistically significant difference in PTA values between any group 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 degrees 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 degrees or more, yet 50% of all domed UKR’s did, as also did 60% of all normal knees.

Conclusions: There is no significant difference in the sagittal plane kinematics of the domed and flat Oxford UKR’s. Both implant designs have a favourable kinematic profile closely resembling the normal knee. The domed knees though do have a greater range of motion under load as compared to the flats, approaching levels seen with the normal knee.

The optimal surgical approach for total hip replacement (THR) remains controversial. We report the clinical outcomes of over 1000 patients in the Exeter primary outcomes study (epos) who underwent primary THR with a cemented Exeter stem (Stryker) but with various acetabular components. This was a prospective non randomised multi centre study. Patient reported hip scores (oxford hip score (OHS)) were measured before operation and at 3 months (n= 1312), 1 (n=1276), 2 (n= 1225), 3 (n=1205) and 4 (n=975) years post operatively. Physician reported scores (Merle d’Aubigne / Postel, MDAP) were measured before operation and at 12 months. All of the operations were carried out using either the anterolateral (Hardinge or modification) or posterior approach.

The posterior approach gave better absolute OHS scores at 3 months and 1 year compared with the anterolateral approach. The improvement in OHS between the pre-op and relevant post-op score was better for the posterior than the Hardinge approach, and this extended to 4 years (all p< 0.05). Early dislocation rates were low in both groups. There was significantly more likely to be heterotopic ossification in the Hardinge group, while stem alignment into varus was more common in the posterior approach group. There was no significant difference between the two approaches as measured using the MDAP score at pre-op or at 12 months after surgery.

These results demonstrate that initial patient perceived clinical benefit of surgery is greater using a posterior than with an anterolateral approach. This should be considered when assessing the best approach for a particular patient. The current results emphasise the value of using patient based outcome measures, as the MDAP score did not detect a difference in outcomes between the two groups.

There has been controversy about the practice of mixing femoral and acetabular implants from different manufacturers in total hip replacement (THR). We studied the clinical outcomes of over 1500 patients in the Exeter Primary Outcomes Study (EPOS) who underwent primary THR with a cemented Exeter stem (Stryker) but with various acetabular components. This was a prospective non-randomised multicentre study. Patient reported hip scores (Oxford Hip Score (OHS)) were measured before operation and at 1 and 2 years post operatively. The choice of acetabular implant was at the surgeons’ discretion. 982 patients had reached four year follow up. Six types of acetabular component were examined (Exeter, Exeter Contemporary, Duraloc (all Stryker), Charnley (DePuy), Cenator (Corin), and Trilogy (Zimmer)).

Patients who received a Charnley cup were found to have worse pre-operative status (significantly higher OHS) than those receiving other cups (especially those receiving Exeter cups) (p< 0.01). Post operatively, this difference continued, with the absolute OHS value remaining greater (i.e. worse clinical result) for the Charnley cup at 1, 2, 3 and 4 years. The association of poor pre-op status with worse post-op result was anticipated. However, when the clinical benefit of surgery (i.e. the improvement in OHS between pre-op and post-op) was assessed, there was no significant difference between the various implants at 1, 2, 3 and 4 years.

These results demonstrate that initial clinical benefit of surgery does not differ between patients receiving acetabular implants from varying manufacturers when the Exeter stem is used. These patients will be followed further to determine whether such “mixing and matching” results in differences in longer term outcomes.

There has been controversy about whether limb length discrepancy (LLD) affects outcome after total hip replacement (THR). We examined input variables and outcomes of over 1200 patients who received primary THR with the Exeter stem and a variety of acetabular components in the Exeter Primary Outcomes Study. This was a non randomized prospective multi centre study.

We examined whether specific groups of patients or surgeons were more likely to have LLD at one year after surgery. Data for leg length measured on clinical assessment were available for 1207 patients at 1 year. 237 patients were recorded as having a leg length difference of 1 cm or more, and 73 a difference of 2 cm or more. 138 were longer on the operated side and 99 were shorter. The likelihood of having LLD of 2 cm or more was not significantly affected by the grade of surgeon (consultant or trainee), BMI, age of patient, position of patient during surgery or surgical approach, or the use of regional or general anaesthetic.

We examined the effect of LLD on outcomes at 3 months and 1,2,3 and 4 years. Patients with LLD > 1cm had significantly worse Oxford Hip Scores (OHS) at 1, 2, 3 and 4 years (p< 0.01), with the OHS generally being an average 2 points worse in those with LLD. The most consistent difference between those with and without LLD was a patient reported limp on the Oxford Hip Questionnaire.

We conclude that LLD is a common problem after THR and that all patient groups may be affected. It is associated with a significantly worse functional outcome as measured by a validated hip score. Systematic adoption of accurate intra-operative measures of leg length might pay dividends in minimizing this complication.

There is concern that patients undergoing total hip replacement by trainee surgeons may do worse than those operated on by consultants. We examined the clinical outcomes of over patients in the Exeter Primary Outcomes Study who underwent primary THR with a cemented Exeter stem (Stryker) with various acetabular components. Over 1400 patients entered the prospective non-randomised multi centre study. Patient reported hip scores (Oxford Hip Score (OHS)) were measured pre operation and at 3 months, 1,2,3 and 4 years post operatively.

The number of patients assessed at 4 years was 982. Trainees operated on patients with worse pre-operative OHS (p< 0.05; t test)) and on significantly less patients under 60 years (p< 0.05 chi square). There was no significant difference in the improvement in OHS (i.e. pre-op OHS – post-op OHS) at any post-operative time point between consultants and trainees. However, patients operated upon by consultants had consistently better postoperative absolute OHS scores (p< 0.05 at 3 months and 1, 2, 3 and 4 years; t test). Complications were low in both groups. Operations performed by trainees lasted longer (mean of 104 vs. 85 minutes). There was also no difference in OHS scores of patients operated by trainees whether they were assisted by an SHO (n=132) or by a consultant (n=249).

In this large cohort of patients there was no difference in the improvement in OHS between patients operated by registrars and consultants. The difference in the absolute OHS values is likely explained by the difference in pre-operative status. We conclude that THRs performed by consultants and by trainees under appropriate supervision give similar initial clinical results. Given current changes to shorten surgical training, it is important that outcomes of THRs performed by future trainees are reviewed to ensure that outcomes are maintained.

The long-term survival of total knee arthroplasty (TKA) has been well established; however, functional outcome remains inconsistent. More normal postoperative TKA kinematics have been shown to produce better knee function. Improved kinematics can be obtained by using implants with optimised surface geometry. Hence a TKA with an appropriate surface geometryis likely to provide superior long-term functional outcome. The Advance-Medial Pivot TKA (Wright Medical) is a fixed bearing prosthesis with a conforming medial compartment and a non-conforming (flat on flat) lateral compartment. This surface geometry is designed with the intention of replicating the normal knee motion of sliding or pivoting medially and rolling back laterally.

Aim: To investigate the sagittal plane kinematics of Advanced Medial Pivot Knee and compare with those of “flat on flat” fixed bearing TKA and normal knees

18 patients who had undergone primary TKA for osteoarthritis were recruited at an average of 18 months post operation. These patients performed flexion and extension exercises against gravity and a step up exercise. Video fluoroscopy of these activities was used to obtain the patellar tendon angle (PTA). This is a previously validated method for assessing sagittal plane kinematics of a knee joint. The kinematic profile of the Advance Medial Pivot Knee was compared to the profile of 14 normal knees and 30 flat on flat, fixed bearing TKA’s.

The sagittal plane kinematics of the Advance TKA differed from the normal knees. However, similarly to normal knees, a linear relationship was observed between PTA and knee flexion angle throughout knee flexion range. The kinematics of the Medial Pivot Knee were similar to normal when the knee was in a highly flexed position.

Functional plane kinematics of the Advance Medial Pivot TKA appear to meet the design criteria in that a linear relationship between PTA and flexion angle is maintained. Further work is required to establish if these improved sagittal plane kinematics translate into improved functional outcome.

Medial unicompartmental replacement (UKR) has been shown to have superior functional results to total knee replacement (TKR) in appropriately selected patients, and this has been associated with a resurgence of interest in the procedure. This may relate to evidence showing that the kinematic profile of UKR is similar to the normal knee, in comparison to TKR, which has abnormal kinematics. Concerns remain over the survivorship of UKR and work has suggested the anterior cruciate ligament (ACL) may become dysfunctional over time. Cruciate mechanism dysfunction would produce poor kinematics and instability providing a potential mechanism of failure for the UKR.

Aim: To test the hypothesis that the sagittal plane kinematics (and cruciate mechanism) of a fixed bearing medial UKR deteriorate over time (short to long term).

A cross sectional study was designed in which 24 patients who had undergone successful UKR were recruited and divided into early (2–5 years) and late (> 9 years) groups according to time since surgery. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint.

This work suggests the sagittal plane kinematics of a fixed bearing UKR is maintained in the long term. There is no evidence that the cruciate mechanism has failed at ten years. However, increased tibial bearing conformity from ‘dishing’, and adequate muscle control, cannot be ruled out as possible mechanisms for the satisfactory kinematics observed in the long term for this UKA.

The indications for unicompartmental knee arthroplasty (UKA) remain controversial; in particular the threshold of disease in the patellofemoral compartment is debated. Whilst some authorities ignore the condition of the patellofemoral joint, others consider pre-existing patellofemoral osteoarthritis (PFOA) a contra-indication to UKA. The aim of this study was to determine the influence of PFOA on the outcome of medial UKA.

This prospective study involved one hundred consecutive patients who had undergone cemented medial Oxford UKA (phase 3), via a minimally invasive approach, at least one year previously. Patients were divided into two groups according to the presence or absence of full thickness cartilage loss (FTCL) on the patella or trochlea at operation. A pre-operative skyline radiograph was graded using the Altman score, by an independent Musculoskeletal Radiologist. Outcome was evaluated with the Knee Society Score (AKSS) and the Oxford Knee Score (OKS, maximum 48). Groups were compared for differences in knee score and Altman grade using a one way ANOVA. Repeat analysis was performed using the presence of anterior knee pain (AKP) as the group defining variable.

There were 28 patients with FTCL, and both groups were well matched for age, gender and activity levels. Analysis showed no significant difference in post operative knee scores between groups with either the presence of FTCL or the presence of AKP pre-operatively as a factor. There was no significant difference in Altman grade between groups.

Intra-operative evidence of PFOA in patients with medial compartment osteoarthritis does not prejudice the outcome of UKA. Even the inclusion of patients with symptomatic AKP, without necessarily having PFOA, does not affect the outcome after UKA. These short results are encouraging, but longer follow up is required.

Functional outcome after patellofemoral joint replacement (PFA) for osteoarthritis remains inconsistent. It is believed that functional outcome for joint replacement is dependent upon postoperative joint kinematics. Minimal disruption of the native joint, as in PFA, should produce more normal kinematics and improved outcome. No previous studies have examined joint kinematics after isolated PFA.

Aim: To investigate the sagittal plane kinematics of patellofemoral replacement and compare with the normal knee.

Twelve patients who had undergone successful PFA at least two years previously were recruited. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. The kinematic profile of the PFA joints was compared to the profiles for fourteen normal knees.

Overall, the kinematic plot obtained for PFA reflected similar trends to that for normal knees; but the PTA was slightly but significantly increased throughout the entire range of flexion (two degrees). This is equivalent to an average displacement of the lower pole of the patella of 1.5mm.

Sagittal plane knee kinematics after PFA are much more normal than after TKR and this should give improved functional outcome. The observed increase in PTA through range may result from increased patella thickness or a shallow trochlear groove and may influence patellofemoral contact forces.

Proprioception protects joints against injurious movements and is critical for joint stability maintenance under dynamic conditions. Knee replacement effect on proprioception in general remains elusive. This study aimed to evaluate the changes in proprioceptive performance after knee replacement; comparing Total (TKA) to Unicompartmental Knee Arthroplasty (UKA).

Thirty-four patients with osteoarthritis were recruited; 15 patients underwent TKA using the AGC prosthesis and 19patients underwent UKA using the Oxford prosthesis. Both cruciate ligaments were preserved in the UKA group, while only the PCL was preserved in TKA patients. Patients’ age was similar in both groups.> Joint Position Sense (JPS) and postural sway were used as measures of proprioception. Both groups were assessed pre- and 6 months post-operatively in both limbs. JPS was measured as the error in actively and passively reproducing five randomly ordered knee flexion angles between 30 and 70°using an isokinetic dynamometer. Postural sway (area and path) was measured during single leg stance using a Balance Performance Monitor. Functional outcome was assessed using the Oxford Knee Score (OKS).

Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb (UKA mean4.64°, SD1.44° and TKA mean5.18°, SD1.35°). No changes in JPS were seen in the control side. A significant improvement (P< 0.0001) in sway area and path was found in the UKA group only in both limbs. No significant changes in sway occurred in either limb of TKA patients. The OKS improved from 21.4 to 35.5 for TKA patients and from 23.9 to 38for UKA patients.

Both UKA and TKA improve proprioception as assessed by JPS. However, UKA alone improves postural sway in both limbs. This may impart explain why UKA patients function better than TKA patients

Oxford Unicompartmental knee arthroplasty (UKA) is now performed using a minimally invasive surgical (MIS) technique. Although early results are encouraging, the studies assessing outcome could be criticised for the restricted number of patients and limited follow-up. Aim of this study was to assess clinical outcome and prosthetic survival rate inpatients with minimally invasive Oxford medial UKA.

This prospective study assessed 500 consecutive patients, who underwent cemented Oxford UKA for medial OA using MIS technique. Patients were assessed using objective and functional Knee Society Score (KSS).

This study has confirmed preliminary findings that Oxford UKA using a minimally invasive approach is safe, reliable and effective.

Introduction: The factors causing chronic instability, a common sequela of ankle inversion sprains are unclear, despite wide investigation. However, few studies have examined potential factors during the injuring movement. We therefore measured the ability of dancers to control ankle movement during quiet stance and after a perturbation into inversion in a group with chronic instability (N=16) and healthy controls (N=26).

Methods: Control of ankle movement was determined by the magnitude of lateral oscillation at the ankle, measured by a 3SPACE Fastrak. The oscillation was measured during single leg stance (baseline oscillation) for two foot positions, flat and demi-pointe. In both positions, the time taken to return to the baseline oscillation after an inversion perturbation (perturbation time) of 15° for the flat foot and 7.5° for the demi-pointe position was also determined.

Results: The baseline oscillation was significantly smaller (P< 0.005) on the demi-pointe for the sprained group (2.5 ± 0.5 mm) than for controls (4.0 ± 2.3 mm). In addition, the perturbation time for the flat foot was significantly longer (P< 0.05) for the sprained group (2.2 ± 0.4 sec) than for controls (1.8 ± 0.5 sec). However, there was a higher (P< 0.05) failure rate among the sprained group for both the perturbation test with the foot flat and for baseline oscillation on the demi-pointe than among the controls.

Conclusions: Our findings demonstrate altered sensorimotor control in chronically unstable ankles. Those sprainers who successfully completed the tasks “braced” the ankle, allowing a small range of oscillation. The increased perturbation time in the sprained group may reflect a deficit in either detection of inversion movements, peroneal muscle response, or both.

Introduction: Numerous studies in the orthopaedic literature have reported changes in knee kinematics following rupture of the Anterior Cruciate Ligament (ACL). Gait analysis is currently the preferred method for studying these in vivo kinematics. The accuracy of this method of analysis remains limited due to errors related to skin movement artefact. Most studies have therefore been limited to analysing subjects performing simple tasks such as straight-line walking, since results become increasingly inaccurate as the subject moves faster. Standard skin marker formats allow measurements of knee flexion angle and varus/valgus angles to be recorded relatively accurately during such tasks. Accurate measurements of rotations and translations at the knee joint, however, are not possible with these set-ups.

Aim: To produce a new method for interpretation of kinematic data from gait analysis, to allow accurate measurement of 3-D displacements at the knee joint during dynamic activity.

Method: We employed two different sets of skin markers in an attempt to increase the accuracy of our data, by diminishing the effects of skin movement. The Kabada¹ marker set was used with retroreflective spheres of 14.5mm diameter. This marker set was used to establish 3-D femoral and tibial co-ordinate systems. We then established a femoral and tibial co-ordinate centre within the distal femur and proximal tibia respectively. A second set of markers was used similar to the “point-cluster” method described by Andriacchi et al². This involved groups of eight smaller spheres (9.5mm diameter) placed in a non-uniform distribution on each of the thigh and shank segments. The positions of all these remaining markers, relative to the co-ordinate centres were then established. 15 subjects were then recorded while performing a series of running and cutting tasks. For each trial that was then analysed, we used all visible markers to optimize the recorded position of the tibial and femoral co-ordinate centres, using a method similar to that described by Soderkvist³. The displacements of these co-ordinate centres were then used to calculate the 3-D tibio-femoral kinematics. Reliability and repeatability tests suggest that this method produces results accurate to 3–4mm.

Conclusion: We believe we have developed a practical and accurate method to analyse 3-D joint kinematics from gait laboratory data.

Purpose This study aims to investigate blood flow in the femoral head during Metal-on-Metal Hip Resurfacing (MMHR) through the posterior approach by monitoring oxygen concentration during the operative procedure.

Methods Following division of fascia lata, a calibrated gas-measuring electrode was inserted into the femoral neck, aiming for the anterolateral quadrant of the head. Baseline oxygen concentration levels were detected after electrode insertion 2–3cm below the femoral head surface and all intra-operative measures were referenced against these. Oxygen levels were continuously monitored throughout the operation. Results of measurements from ten patients are presented.

Results Oxygen concentration was reduced during the surgical approach and average oxygen concentration following dislocation and circumferential capsulotomy dropped to 43% of baseline (Std.dev +/−37%), this was a highly significant reduction (p< 0.005). Insertion of implants resulted in a further significant drop in oxygen concentration (p< 0.02) to 16% of baseline (Std. dev +/−27%). Oxygen concentration rose slightly after relocation of the resurfaced joint and reconstruction of posterior soft tissues, reaching 22% (Std.dev +/−31%) of initial baseline oxygen levels. Considerable variation between subjects was observed. Three subjects had no remaining oxygen concentration at the end of surgery.

Conclusion Intra-operative measurement of oxygen concentration in blood perfusing the femoral head is feasible. During MMHR there is a dramatic decrease in femoral oxygenation during surgical approach and implant fixation. This may increase the risk of avascular necrosis and subsequent femoral neck fracture. Future experiments will determine if less invasive procedures or a different approach can protect the blood supply to femoral neck and head.

Introduction: Knee joint arthroplasty (total or unicompartmental) is the standard operative treatment for osteoarthritis (OA). Survival rate is good for both types but functional outcome is different. The function of unicompartmental knee arthroplasty (UKA) is substantially better than that of total knee arthroplasty (TKA). As function can be strongly influenced by proprioceptive ability, it is possible that improved outcome seen in patients with UKA results from retaining proprioceptive function associated with the cruciate ligaments. This prospective longitudinal study aimed to evaluate the change in proprioceptive performance after knee replacement; comparing TKA to UKA.

Methods and Materials: Two groups of patients with OA as diagnosed clinically and by X-ray were recruited. Group 1 consisted of 15 patients (mean age 65.8 years range 57–72 years, 10 females and 5 males) listed for TKA with the AGC prosthesis (Biomet, UK). Group 2 consisted of 19 patients (mean age 65.5 years range 52–75 years; 9 females and 10 males) listed for UKA with the Oxford UKA (Biomet, UK) for medial compartment OA. The ACL and PCL were present and preserved in all patients in Group 2, while only the PCL was preserved in Group 1 patients. Joint Position Sense (JPS) and postural sway were used as measures of proprioception performance. Both groups were assessed pre-and 6 months post-operatively in both limbs. JPS was measured using a dynamometer (KinCom, Chatanooga Ltd) as the error in actively and passively reproducing five randomly ordered knee flexion angles (30°, 40°, 50°, 60° and 70°). Postural sway (area, path and velocity) was measured during single leg stance using a Balance Performance Monitor (SMS Medical) for 30 seconds interval. Functional outcome was assessed using the Oxford Knee Score (OKS).

Results: Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb only (Mean ± standard deviation for UKA 4.64±1.44° and for TKA 5.18±1.35°). No changes in JPS were seen in the control side. An improvement in sway was found in the UKA group only. UKA patients showed significant improvement in both sway area and path (p< .0001) for both limbs post-operatively. No significant post-operative changes in sway occurred in either limb of TKA patients. The OKS improved postoperatively in both groups, rising from 21.4 to 35.5 for TKA patients and from 23.9 to 38 for UKA patients.

Conclusion: Interestingly, joint position sense improved for both groups but did not seem to show any difference between UKA and TKA. Postural sway was influenced by joint replacement type. Ligament retention may contribute to improved global postural control seen after unicompartmental knee arthroplasty and may explain the higher level of function seen in these patients.

Aims: The purpose of this study is to determine the causes of failed medial Oxford unicompartmental knee arthroplasty (UKA) and assess the outcome after revision surgery.

Materials And Methods: From 1993 to 2003, sixty-nine Oxford UKA (58 patients) were revised to a total knee replacements (TKR) at this centre. The type of implant used at revision surgery, pre- and post-revision American Knee Society (AKS) and Tegner scores were analyzed retrospectively.

Results: The patient’s mean age at the time of UKA was 64.5 years (range: 50–79). The average pre-revision scores were as follows: AKS-Objective score was 41.2 (± 10.4), the AKS-functional score was 56.8 (±10.0) and the average Tegner score was 1.5 (±0.6). The mean follow-up period was 38.3 (range: 12–107) months. The common causes of failure were: lateral compartment osteoarthritis (34.0%), component loosening (30.4%) and early or late infection requiring two-stage revision surgery (14.3%). The majority were revised using a standard primary TKR implant and only six (9%) requiring augmentation stems. Patellar resurfacing was performed in 25% of cases. The mean polyethylene liner width of the revision TKR was 13.4mm (±3.7). The average post-revision scores were: AKS-Objective score 77.4 (±13.1), the AKS-functional AKS score 70 (±21.1) and the average Tegner score of 2.2 (±0.8). Three knees needed rerevision for infection of the revised implant.

Conclusions: Lateral compartment osteoarthritis was the commonest indication for revision surgery for a failed medial Oxford UKA. Revision of a UKA is technically easier and the results are superior to the published results of revision of a primary TKR. In more than 90% cases, no augmentation or stemmed implants were necessary.