Elimination of Preoperative Flexion Contracture as a Contraindication for Unicompartmental Knee Arthroplasty.

INTRODUCTION: Unicompartmental knee arthroplasty (UKA) is an effective alternative to total knee arthroplasty (TKA) for the management of unicondylar osteoarthritis. Historical contraindications limit patients' eligibility for UKA. However, recent reports have suggested that some contraindications may not be absolute. This study evaluates preoperative flexion contracture with regard to UKA. METHODS: This study was a retrospective review of 53 patients with preoperative flexion contracture between 11° and 20° who underwent fixed-bearing UKA and a matched cohort of 53 patients who underwent cruciate-retaining TKA. RESULTS: Preoperatively, the average flexion contracture was 13.8° in the UKA group and 14.1° in the TKA group (P = 0.42). Mean preoperative motion was greater in the patients treated with UKA (106°) than in those treated with TKA (97°; P < 0.001). Postoperatively, patients who underwent UKA had greater motion than patients who underwent TKA had (121° versus 113°; P < 0.01). Residual flexion contracture was greater in the UKA group (4.1°) than in the TKA group (2.1°; P = 0.02). The two groups demonstrated similar improvements in Knee Society clinical scores (P = 0.32). However, patients treated with UKA demonstrated higher Knee Society functional scores, compared with patients treated with TKA (86 versus 75; P = 0.03). DISCUSSION: Although residual flexion contracture was worse after UKA, this group had similar clinical improvement, greater postoperative motion, and greater function scores, compared with the matched TKA group. Preoperative flexion contracture >5° may not be an absolute contraindication to UKA. CONCLUSION: The contraindications to UKA regarding flexion contracture may not be as absolute as previously thought. Larger, prospective studies are needed to generalize these findings to a wider population.

Is Outpatient Unicompartmental Knee Arthroplasty Safe to Perform at an Ambulatory Surgery Center? A Comparative Study of Early Post-Operative Complications.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) lends itself to the outpatient surgical setting. Prior literature has established a low rate of readmission and post-operative complications when performed in a hospital outpatient setting (HOP). To our knowledge, there have been no studies comparing complications of UKA performed at an ambulatory surgery center (ASC) and those in a HOP. METHODS: We retrospectively reviewed all patients who underwent outpatient UKA by a single surgeon from 2012 to 2016. In all 569 outpatient UKAs were performed: 288 in the ASC group and 281 in the HOP group. We compared the groups with regard to all complications within the first 90 days after surgery. RESULTS: Thirty minor and major complications occurred within 90 days (5.3%). There was no difference in the overall complication rate between groups (ASC 12, 4.2%; HOP 18, 6.4%) (P = .26). Day of surgery admission occurred once in the HOP group (0.4%) and did not occur in the ASC group (P = .49). There was 1 visit to the emergency department (ED) <24 hours from surgery in each group (ASC 0.3%, HOP 0.4%) (P = 1.0). ED visits occurred within 7 days in 3 ASC cases (1.0%) and 4 HOP cases (1.4%) (P = .72). Re-admissions in the first 90 days occurred in 5 ASC cases (1.7%) and 8 HOP cases (2.8%) (P = .41). CONCLUSION: UKA at an ASC has a low early postoperative complication rate without increased risk of re-admission or ED evaluation when compared to UKAs performed at a HOP.

Patellar Cut and Composite Thickness: The Influence on Postoperative Motion and Complications in Total Knee Arthroplasty.

BACKGROUND: Little data exist on the influence of patellar thickness on postoperative motion or complications after total knee arthroplasty (TKA). This study addresses the following questions: Is postoperative motion influenced by change in composite patellar thickness? Is change in patellar thickness associated with more complications? And do more complications occur in the knees with a patellar bone remnant (<12 mm) and a native patellar thickness <18 mm? METHODS: In total, 3655 TKAs were performed by 3 surgeons over a 28-year interval. All knees had caliper measurement of patellar thickness before the patellar cut, after implantation of the component and postoperative motion recorded in the database 1 or 2 years after TKA. RESULTS: Patellar composite thickness was the same (1034 knees), thicker (1617 knees), and thinner (1004 knees). A significant but weak relationship was identified between the change in patellar thickness and motion (P < .01, ρ = -0.046); an increase in "composite patellar thickness" of 10 mm would result in a 3° loss of knee motion. Significant differences were identified between change in thickness and manipulations (P < .05), ruptures (P = .01), and patellar clunk/crepitus (P < .01). Examining knees with bone remnant thicknesses (<12 mm/≥12 mm), there was no difference in fractures (P = .26). No extensor ruptures occurred in knees with remnant thickness <12 mm. Comparing knees with native bone thickness (≤18 mm/>18 mm), significant differences were found in fractures (P < .01) and patellar radiolucencies (P = .01). CONCLUSION: As this data does not demonstrate a strong tendency toward losing motion when the patellar thickness is increased, the authors recommend avoiding compromise of the patellar bone stock and tendon insertion. When native patellar bone is thin (<18 mm), we recommend maintaining 12 mm of patellar bone stock and accept the increase in composite thickness.

Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.

BACKGROUND: Historically, a functional ACL has been a prerequisite for patients undergoing unicondylar knee arthroplasty (UKA). However, this premise has not been rigorously tested. QUESTIONS/PURPOSES: We compared (1) the survivorship free from revision and (2) the failure mechanisms of UKAs in ACL-deficient knees and UKAs in ACL-intact knees performed over the same time interval. METHODS: Between November 2000 and July 2008, a fixed bearing UKA was performed in 72 patients (81 knees) with intraoperatively confirmed ACL deficiency. Five patients (five knees) with preoperative instability underwent ACL reconstruction and were excluded from analysis. Of the remaining 67 patients (76 knees) without preoperative instability, implant status was known for 68 UKAs in 60 patients. Survivorship and failure mechanisms for these knees were compared to those of 706 UKAs in ACL-intact knees performed during the same time interval by the same surgeon using the same implant system. Minimum followup for the ACL-deficient group was 2.9 years (mean, 6 years; range, 2.9-10 years). RESULTS: Revision rates between UKAs with and without intact ACLs were similar in the absence of clinical instability (p = 0.58). Six-year UKA survivorship was 94% (95% CI: 88%-100%) in ACL-deficient knees and 93% (95% CI: 91%-96%) in ACL-intact knees (p = 0.89). Five knees (7%) in the ACL-deficient group were revised: disease progression (two), loose tibia (one), persistent pain (one), and revised elsewhere/reason unknown (one). Thirty-six knees in the ACL-intact group underwent revision (5%): aseptic loosening (13), revised elsewhere/reason unknown (11), disease progression (three), tibial subsidence/fracture (four), infection (three), pain (one), and lateral compartment overload (one). CONCLUSIONS: At 6 years, deficiency of the ACL in patients without clinical knee instability did not impact the survivorship of UKAs compared to UKAs performed in knees with intact ACLs.

Mid-term survivorship of minimally invasive unicompartmental arthroplasty with a fixed-bearing implant: revision rate and mechanisms of failure.

Minimally invasive unicondylar arthroplasty (UKA) continues to gain popularity for the management of patients with degenerative arthritis limited to one compartment of the knee. In this study, we examine a series of 517 fixed-bearing, cemented unicompartmental knee components implanted in patients to manage degenerative arthritis in the medial compartment of their knee. All UKAs were performed at a single institution using the same fixed-bearing design. In this study we sought to examine the survivorship of the UKA components and the mechanisms of failure for the knees that were revised. The survivorship and revision rate with this implant were similar to those found in other published reports of fixed-bearing unicompartmental arthroplasties performed through minimally invasive surgical techniques.

The functional assessment test: a method of evaluating improvement in function after knee arthroplasty.

Questionnaires are marginally useful for objectively measuring function after knee arthroplasty. The Functional Assessment (FA) test is an easily administered, timed test of a person's ability to stand, walk and ascend/descend stairs that would be useful for quantifying a patient's function after knee arthroplasty. Four hundred forty-five individuals were included in the study: 313 without lower extremity arthritis or neurologic disease and 132 with advanced degenerative arthritis prior to knee arthroplasty. As expected, the test times were longer for individuals afflicted with knee arthritis. Arthroplasty patients were tested pre- and postoperatively to determine if their FA test time improved. The FA test takes less than a minute and is practical for use in the clinical setting as a simple means of quantifying function before and after knee arthroplasty.

Use of structural allograft in revision total knee arthroplasty in knees with severe tibial bone loss.

BACKGROUND: Tibial bone loss is frequently encountered at the time of revision total knee arthroplasty, and the outcome of the revision often depends on the management of this bone deficiency. We examined the clinical and radiographic outcomes of a series of revision total knee arthroplasties in which a structural allograft had been used to reconstruct a tibial bone defect encountered at the time of the revision procedure. METHODS: From January 1985 through September 1999, one surgeon performed revision arthroplasty in forty-nine knees (forty-seven patients) with a severe tibial bone defect. The reasons for the revisions included polyethylene wear and osteolysis in twenty-four knees, aseptic loosening in seventeen knees, infection in five knees, and failure for another reason for three knees. Structural allograft was used alone in thirty-five knees and in conjunction with a tibial augment in fourteen knees. The mean age of the patients at the time of the revision arthroplasty with the allograft was sixty-seven years. The patients were assessed clinically with use of the Knee Society score and radiographically. RESULTS: The status of the implant was known for forty-six of the forty-nine knees in this study. It was unknown for one patient (one knee) who was lost to follow-up and for two patients (two knees) who died less than five years postoperatively. Four revision procedures in four patients failed and required a reoperation. Two of the failures were due to infection. At a mean of ninety-seven months postoperatively, the mean Knee Society clinical score was 84 points for the knees that had not had a reoperation due to failure. The mean arc of motion improved from 87 degrees preoperatively to 103 degrees at the most recent follow-up evaluation. Histological evaluation of specimens retrieved at two autopsies demonstrated graft union to host bone. CONCLUSIONS: A structural allograft provides a stable and durable reconstruction of a tibial bone deficiency. At a mean of ninety-five months postoperatively, we found no instance of graft collapse or aseptic loosening associated with the structural allograft. We recommend the use of a structural allograft for the management of severe tibial bone deficiency at the time of revision total knee arthroplasty.

Wear and osteolysis around total knee arthroplasty.

Osteolysis induced by wear debris of ultra-high-molecular-weight polyethylene has emerged as a significant problem after total knee arthroplasty. The generation of polyethylene wear and the development of osteolysis around total knee arthroplasty are caused by a combination of patient, implant, and surgical factors. Activity level over time may be the most important patient factor affecting the loads placed on a total knee replacement, but it is the most difficult to manage. Multiple factors related to the manufacturing of the polyethylene implant influence the extent of wear, and surgeons should be cautious in considering enhanced polyethylenes pending results of further investigations. The optimal design of the articular bearing surface remains controversial but needs to be considered with respect to the stresses imparted on component-bone and modular tibial backside interfaces. Surgical factors, including restoration of alignment and ligament balance, are important for long-term durability of the implant. Methods of measuring the wear of total knee implants are still evolving. Thus, when confronted with a worn total knee implant and developing osteolysis, the surgeon should consider each of these factors in selecting the best management option to eliminate the source of debris and minimize the potential for wear and osteolysis following revision.

Isolated revision of failed metal-backed patellar components: outcome with minimum 4-year follow-up.

Several reports document high failure rates of metal-backed patellar components, but few report the outcome of revising these components to all-polyethylene, cemented implants. At a mean 87.2-month follow-up, we describe a series of 36 patients (40 knees) who underwent isolated metal-backed patellar revision to a cemented, all-polyethylene patellar component. After the patellar revision, 5 patients (6 knees) underwent additional surgery, but no patellar components required revision. The additional surgeries were performed at an average of 77.6 months after patellar revision and included 3 tibial insert exchanges for polyethylene wear, 2 revisions of femoral and tibial components for osteolysis, and 1 realignment procedure for recurrent subluxation of the patella. We conclude that revision of a failed metal-backed patellar component to a cemented, all-polyethylene patella is a durable, successful procedure.

Treatment of the unstable total knee arthroplasty.

Instability is one of the leading causes of clinical failure after total knee arthroplasty. Instability can be categorized according to three basic patterns: AP or flexion space instability, varus/valgus or extension space instability, and global instability. Surgical options for treating instability include polyethylene exchange of a modular component, revision to a more constrained component, or revision to a hinged component. The results achieved with these surgical options vary for each type of instability. In general, the use of more constrained components to manage unstable knees is favored.

Epidemiology of osteolysis: backside implant wear.

Osteolysis is an emerging problem in patients who undergo total hip arthroplasty and total knee arthroplasty (TKA). Before the introduction of modular components, osteolysis was not as prevalent in patients who underwent TKA. Although polyethylene wear and the generation of small-particle debris were linked to the presence of osteolysis in patients who have undergone total hip arthroplasty, the fatigue-type wear and larger wear particles often seen with TKA were not thought to invoke the cellular response that causes osteolysis. Despite the lack of an identifiable cause for the osteolysis, the number of knees that developed lesions continued to increase. Therefore, modular components were examined to determine whether this innovation in TKA was actually contributing to the manifestation of osteolysis.

Synovial entrapment: a complication of posterior stabilized total knee arthroplasty.

BACKGROUND: We observed a complication of posterior stabilized total knee arthroplasty involving hypertrophy of tissue proximal to the patella associated with pain during active knee extension from 90 degrees of flexion. The purpose of this paper was to describe synovial entrapment and to determine if design features of the prosthesis predispose patients to the complication. METHODS: Between April 1990 and June 1999, we performed 459 consecutive posterior stabilized primary total knee arthroplasties using three prosthetic designs with different femoral intercondylar geometries. We identified twenty-six patients (twenty-seven knees) in whom arthroscopic débridement of the knee or open arthrotomy with débridement of the knee had been subsequently performed because of a diagnosis of synovial entrapment. We reviewed the records of these patients to identify the knee components that had been used and the symptoms and conditions that necessitated additional treatment. RESULTS: Symptoms (grating, crepitation, and pain with active knee extension from 90 degrees) necessitating subsequent débridement occurred in 13.5% (nineteen) of 141 knees treated with the Anatomic Modular Knee-Congruency implant, 3.8% (eight) of 212 treated with the Anatomic Modular Knee-Posterior Stabilized implant, and none of the 106 treated with the Press Fit Condylar Sigma-Posterior Stabilized implant. All patients had difficulty rising from a chair and climbing stairs; however, none had symptoms when standing or walking. No patient had a patellar clunk. The symptoms occurred at a mean of seven months after the arthroplasty in the patients with an Anatomic Modular Knee-Congruency implant and at a mean of twenty months after the arthroplasty in those with an Anatomic Modular Knee-Posterior Stabilized implant. Débridement of the frond-like hypertrophic synovial tissue at the distal aspect of the quadriceps tendon alleviated symptoms in all patients. No nodules were identified during the arthroscopy. CONCLUSIONS: Synovial entrapment is characterized by hypertrophic synovial tissue at the superior pole of the patella. Use of a posterior stabilized femoral component with a proximally positioned or wide femoral box is more likely to result in this complication.

Rapid polyethylene failure of unicondylar tibial components sterilized with gamma irradiation in air and implanted after a long shelf life.

BACKGROUND: The mechanical toughness of polyethylene that has been sterilized by gamma irradiation in air decreases after a long shelf life. The purpose of the present study is to report the high failure rate after unicondylar knee replacements performed with polyethylene bearings that had been sterilized with gamma irradiation in air and implanted after a shelf life of < or = 4.4 years. METHODS: Between December 1997 and January 2000, seventy-five unicondylar knee replacements were performed in sixty-two patients. All patients were followed both clinically and radiographically. A revision operation was offered when the patient had pain, swelling, and radiographic evidence of rapid polyethylene wear. The effect of aging of the polyethylene during storage was evaluated by dividing the knees into three groups on the basis of shelf life and comparing them with regard to the rate of revision and the observed wear of the polyethylene. Four retrieved components were examined for the presence of oxidation. RESULTS: At a mean of eighteen months after the arthroplasty, thirty knees had been revised and seven were scheduled for revision. The rate of polyethylene wear increased as the shelf life increased. There was a significant inverse linear correlation between the shelf life of the polyethylene and the time to revision (p < 0.01, r (2) = 0.64). All retrieved components had greater-than-expected wear with pitting and delamination of the surface. Seven components had fractured, and ten had both fractured and fragmented. Analysis of four components confirmed severe oxidation of the polyethylene. CONCLUSION: The present study demonstrated early, severe wear of tibial polyethylene bearings that had been sterilized by gamma irradiation in air and stored for < or = 4.4 years. This risk can be minimized by ensuring that implants have not been sterilized with gamma irradiation in air and stored for several years.