Introduction

Studies have shown that increased implant conformity in total knee arthroplasty (TKA) has been linked to increased constraint and thus rotational torque at the bone/implant interface. Anterior stabilized (AS) tibial inserts were designed to compensate for excessive AP motion in less-conforming cruciate-retaining (CR) tibial inserts. However, increased constraint may affect implant loading. Therefore, the purpose of this study is to model rotational prosthesis constraint based on implant-specific data and to compare rotational torque and 3D contact forces in implants with CR-lipped and AS tibial inserts during normal gait.

The brief answer is no….I do not believe that outpatient total joint arthroplasty is the emergent standard of care. However, for some patients and some surgeons I do believe that outpatient total joint arthroplasty can be performed safely and with greater comfort and convenience for the patient. Further, for the surgeon, it can provide greater control over the care environment if performed at an ambulatory surgery center.

Patient selection is paramount in my opinion for safely performing outpatient total joint arthroplasty. While some have attempted to define specific criteria, our own criteria include patients with simple orthopaedic problems who are healthy, trustworthy and have a good support system of family or friends to assist them.

As surgeons we must also be self-aware as the margin for error, particularly at a freestanding ambulatory surgery center, is narrow. Operative times should be reliably brief and blood loss should be minimal to allow for a safe discharge on the same day. Further the incidence of intraoperative complications such as fractures at the time of total hip arthroplasty or ligament injuries during total knee arthroplasty should be low. The surgeon should also be prepared with the equipment to address these common issues, if they do occur.

In our review of the NSQIP data set we matched 1,236 outpatient TJA 1:1 with inpatients based on propensity scores. The risk of 30-day readmissions and complications was no different between groups, although inpatients had a higher rate of VTE and outpatients had a higher risk of re-operation. Risk factors for adverse events included patient age > 85 years old, diabetes and BMI > 35. Likewise in a review of results from my own practice, we have seen no difference in the risk of complications.

As health care providers we must keep the safety of our patients paramount at all times. Further, we must be fiscally responsible to avoid costly complications, reoperations and readmissions. With conservative patient selection and careful surgical technique I believe that outpatient TJA offers an attractive alternative that is safe, cost effective and associated with high satisfaction for both patients and surgeons.

The AAOS clinical practice guideline for diagnosis of periprosthetic joint infection (PJI) and the MSIS definition of PJI were both “game changers” in terms of diagnosing PJI and the reporting of outcomes for research. However, the introduction of new diagnostic modalities, including biomarkers, prompted a re-look at the diagnostic criteria for PJI. Further there was a desire to develop an evidence-based, validated algorithm for the diagnosis of PJI.

This multi-institutional study led by Dr. Jay Parvizi examined revision total joint arthroplasty patients from three academic institutions. For development of the algorithm, infected and aseptic cohorts were defined. PJI cases were defined using only the major criteria from the Musculoskeletal Infection Society (MSIS) definition (n=684). Aseptic cases underwent revision for a non-infective indication and did not show evidence of PJI or undergo a reoperation for any reason within 2 years (n=820). Risk factors, clinical findings, serum and synovial markers as well as intraoperative findings were assessed. A stepwise approach using random forest analysis and multivariate regression was used to generate relative weights for each of the various variables assessed at each stage to create an algorithm for diagnosing PJI using the 3 most important tests from each step. The algorithm was formally validated on a separate cohort of 422 patients, 222 who were treated with a 2-stage exchange for PJI who subsequently failed secondary to PJI within one year and 200 patients who underwent revision surgery for an aseptic diagnosis and had no evidence of PJI within two years and did not undergo a reoperation for any reason.

The first step in evaluating PJI should include a physical examination to identify a sinus tract, followed by serum testing for C-reactive protein (cut-off value 1mg/dl), D-dimer (cut-off value 860ng/mL) and/or erythrocyte sedimentation rate (cut-off value 30mm/hr) in that order of importance. If at least one of these are elevated, or if there is a high clinical suspicion, joint aspiration should be performed, sending the fluid obtained for a synovial fluid white blood-cell (cut-off value 3,000 wbc/uL) or leukocyte esterase strip testing, polymorphonuclear percentage (cut-off value 80%) and culture. Alpha defensin did not show added benefit as a routine diagnostic test.

Major diagnostic criteria are the same whereby the presence of a sinus tract or (2) positive cultures showing the same organism defines PJI.

Special care should be taken in cases of ALTR (failed metal-on-metal bearing), crystalline deposition disease, inflammatory arthritis flares or slow growing organisms.

In the rare cases where no fluid is obtained at the time of an attempted aspiration and revision surgery is not planned, then this is the rare scenario where nuclear imaging (my preference is an indium labeled white blood cell scan) or a biopsy can be performed.

The updated definition of PJI demonstrated a higher sensitivity of 97.7% when compared to the MSIS criteria (79.3%) and the ICM definition (86.9%), with a similar specificity of 99.5%. However, just over 2% of patients examined do fall into the “inconclusive” category.

The proposed diagnostic algorithm demonstrated a high overall sensitivity (96.9%) and specificity (99.5%).

Unicompartmental knee arthroplasty (UKA) has a long history that extends back nearly as far as the first tricompartmental designs. While initial results were erratic, with a greater understanding of patient selection and surgical techniques, more consistent and favorable results have been reported. While there has been somewhat of a resurgence in interest in UKA, the percentage of primary knee arthroplasties that are unicompartmental hovers around 6–8%. It is my belief that you should be doing more!

Several peer review studies suggest that with both fixed and mobile bearing designs, survivorship exceeds 90% at ten year. In our own initial series of 62 fixed bearing medial UKA, survivorship was 90% at 20 years.

UKA is an outstanding option for younger patients, who are amongst the most challenging to satisfy with a TKA. In a cohort of patients < 55 years old, Biswas et al. reported a mean KSS of just over 95 points and a mean UCLA activity score of 7.5. This is opposed to the report by Parvizi et al. who suggested 1/3 of young, active patients reported residual symptoms and limitations following modern TKA.

Most data suggests that UKA is a less morbid procedure than TKA. In a retrospective review of 605 UKA compared to 2235 TKA, Brown et al. found the risk of complications was 11% vs. 4.3% favoring UKA with a shorter length of stay and risk of discharge to an extended care facility, which also translates into lower costs for our health care system.

Finally, in the only randomised study that I am aware of that has compared UKA and TKA, UKA was associated with significantly better survivorship (90% vs. 79%). Further, UKA was associated with better ROM and functional scores at 5 and 15 years. Finally, recovery with UKA was faster and the risk of peri-operative complications was lower.

As with any revision knee arthroplasty, the first rule of revision is to ensure that the reason for failure has been identified, as revision for pain alone is associated with poor results. This is particularly important when considering revision of a UKA, as surgeons may have a lower threshold for revision than following TKA given the perception that the revision is “easy” and that the pain is “probably from the unresurfaced compartments”.

In a multi-center study, we found that many patients undergoing revision of a failed UKA do not have an appropriate evaluation for infection. Evaluation should include a screening ESR and CRP and if abnormal, an aspiration of the knee joint for synovial fluid WBC count, differential and culture.

To revise a UKA to a TKA, we perform the revision as we would a primary TKA, ignoring the implanted femoral component and using it to assist with reference of femoral component rotation and for the distal femoral cut; the component is not removed until it must for the final preparation. After finishing the femoral component cuts, the tibia is completely exposed prior to carefully removing the tibial component and re-cutting the tibia. In our experience of 45 consecutive both component revisions of UKA to TKA at Rush, 44 used primary implants (98%), including cruciate retaining implants in 36 of these 44 knees (82%; the balance were PS implants) and tibial stems were utilised in 6 of 44 knees (14%).

In order to better understand the outcomes of revision of failed UKA we studied 49 patients revised from UKA to TKA and 43 revised from HTO to TKA and matched them to 43 aseptic, both component revision TKA and 97 primary TKA. At a mean of 4.8 years, the KSS and Function Scores in the UKA to TKA, HTO to TKA and primary TKA cohorts were similar. Total operative times were significantly higher in the HTO to TKA and revision TKA groups. Length of hospital stay was shorter in the primary TKA cohort. The rate of complications and reoperations were higher in the HTO to TKA and revision TKA groups compared to the UKA to TKA and primary TKA groups. Based on these results, we believe that revising an HTO and UKA to a TKA both had functional outcomes more similar to a primary than a revision TKA, however, the complication rate of revising an HTO was more similar to a revision than a primary TKA.

Recurrent dislocation following total hip arthroplasty (THA) is a complex, multifactorial problem that has been shown to be the most common indication for revision THA. At our center, we have tried to approach the unstable hip by identifying the primary cause of instability and correcting that at the time of revision surgery.

Type 1: Malposition of the acetabular component treated with revision of the acetabular component and upsizing the femoral head.

Type 2: Malposition of the femoral component treated with revision of the femur and upsizing the femoral head.

Type 3: Abductor deficiency treated with a constrained liner or dual mobility bearing.

Type 4: Soft tissue or bony impingement treated with removal of impingement sources and upsizing the femoral head.

Type 5: Late wear of the bearing treated with bearing surface exchange and upsizing the femoral head.

Type 6: Unclear etiology treated with a constrained liner or dual mobility articulation.

The most common etiologies of instability in our experience include cup malposition (Type 1) and abductor deficiency (Type 3).

We reviewed 75 hips revised for instability and at a mean 35.3 months, 11 re-dislocations occurred (14.6%). Acetabular revisions were protective against re-dislocation (p<0.02). The number of previous operations (p=0.04) and previously failed constrained liners (p<0.02) were risk factors for failure. The highest risk of failure was in patients with abductor insufficiency with revisions for other etiologies having a success rate of 90%.

Although instability can be multifactorial, by identifying the primary cause of instability, a rational approach to treatment can be formulated. In general, the poorest results were seen in patients with abductor deficiency. Given the high rate of failure of constrained liners (9 of the 11 failures were constrained), we currently are exploring alternatives such as dual mobility articulations. Our early experience with dual mobility suggests improved results when compared to constrained liners.

Revision of the failed femoral component of a total hip arthroplasty can be challenging. Multiple reconstructive options are available and the operation itself can be particularly difficult and thus meticulous pre-operative planning is required to pick the right “tool” for the case at hand. The Paprosky Femoral Classification is useful as it helps the surgeon determine what bone stock is available for fixation and hence, which type of femoral reconstruction is most appropriate.

Monoblock, fully porous coated diaphyseal engaging femoral components are the “work-horse” of femoral revision and are used in my practice for approximately 70% of reconstructions. These stems are associated with problems, in the following situations: The canal diameter is greater than 18mm; There is less than 4cm available for distal fixation in the isthmus; There is proximal femoral remodeling into retroversion.

When the limits of monoblock stems are exceeded, we use modular tapered femoral components. These stems in general allow for better fixation in short isthmic segments and the bi-body nature allows for independent positioning of the proximal body, which is particularly helpful when the femur has remodeled into retroversion.

Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip arthroplasties in the United States. Hence, there is great interest in maximising stability to prevent this complication.

Highly cross-linked polyethylene has allowed us to increase femoral head size, without a clinically important increase in wear. Head size has long been recognised to have a strong influence on the risk of dislocation postoperatively. As femoral head size increases, stability is augmented, secondary to a decrease in component-to-component impingement, which is theoretically eliminated at head sizes greater than 36mm in diameter (however osseous impingement can still occur). Larger head sizes also greatly increase the “jump distance” required for the head to dislocate (in an appropriately positioned cup) and eliminate the need for skirts. Level one studies support the use of larger diameter heads as decreasing the risk of dislocation following primary and revision THA.

Larger diameter heads do, however, have negatives with the most recent concern being larger forces imparted upon the trunnion, which may contribute to adverse local tissue reactions (ALTR) which have recently been reported in patients with a metal on polyethylene bearing. However, in the series by Cooper et al, 32mm was the most common head size identified with no head sizes >36mm in this series. This suggests that the cause of ALTR is probably multifactorial and while femoral head size may be a contributor, the trunnion itself may be more important including its diameter, length and modulus of elasticity as well as the specific finish of the taper. Finally, when larger femoral head sizes are used in smaller acetabular components, the result is a thinner polyethylene liner, which may increase the risk of liner breakage. Larger diameter bearings may also increase the risk of squeaking in ceramic on ceramic bearing couples.

Hence, the decision on femoral head size probably should include a balance between patient risk factors for instability and the risks of increased head size. Hence for revision procedures, and in primary cases where the risk of dislocation is known to be high, the risk of a larger femoral head is probably outweighed by the benefits of enhanced stability if a larger femoral head is utilised.

Introduction

This study compares the incidence of post-operative complications (within 90 days) following primary total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA).

Introduction

Modular tapered implants have been suggested as the optimal treatment in patients with severe femoral bone loss undergoing revision total hip arthroplasty (THA). The purpose of this study is to describe minimum 2 year follow up of patients treated with modular tapered prostheses for Paprosky type IIIB and IV femoral bone loss in revision THA.

Introduction

When using press-fit stems in revision total knee arthroplasty (TKA), diaphyseal engagement optimizes stability. Attempts to maximize press fit may lead to periprosthetic fracture; however, the literature offers no guidance regarding the prevalence or management of this complication. The purpose of this study is to report the incidence, risk factors, and outcomes of these fractures.

Introduction

Serum erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and synovial fluid white blood cell (WBC) count and differential are effective in diagnosing periprosthetic joint infection (PPJI); however their utility in patients with inflammatory arthritis is unknown. The purpose of this study is to determine the utility of these tests in patients with inflammatory arthritis.

INTRODUCTION

The purpose of this study was to determine the rate of complications and re-operations after operative treatment of peri-prosthetic femur fractures sustained within 90 days following primary total hip arthroplasty (THA).