Characterizing the Magnitude of and Risk Factors for Functional Limb Lengthening in Patients Undergoing Primary Total Knee Arthroplasty.

Background: There is little data on the magnitude and factors for functional leg lengthening after primary total knee arthroplasty (TKA). Questions/Purpose: We sought to determine the incidence of and risk factors for functional leg lengthening after primary TKA. Methods: We retrospectively reviewed consecutive unilateral primary TKAs at a single institution from 2015 to 2018. Of the 782 TKAs included, 430 (55%) were performed in women; the mean age was 66 years, and the mean body mass index was 29 kg/m2. Preoperatively, 541 (69%) knees were varus deformities and 223 (29%) were valgus deformities. Hip to ankle biplanar radiographs were obtained preoperatively and 6 weeks postoperatively for all patients. Two independent researchers measured leg length, coronal plane deformity, lateral knee flexion angle, and overall mechanical alignment on all preoperative and postoperative radiographs. Results: The mean overall ipsilateral functional leg lengthening was 7.0 mm. Seven hundred knees (90%) were overall functionally lengthened, including 462 (59%) knees lengthened >5 mm and 250 (31%) knees lengthened 10 mm or more. A valgus deformity and coronal plane deformity of 10° or more were significant risk factors for increased functional lengthening. Patients with severe valgus deformities (>10°) had the largest amount of functional lengthening, at a mean of 13.5 mm. Conclusion: After primary TKA, 90% of limbs are functionally lengthened, including roughly one-third over a centimeter. Valgus knee deformities and severe deformities (>10°) were significant risk factors for increased limb lengthening.

Three Degrees External to the Posterior Condylar Axis Has Little Relevance in Femoral Component Rotation: A Computed Tomography-Based Total Knee Arthroplasty Simulation Study.

BACKGROUND: Femoral component rotation in total knee arthroplasty (TKA) has a significant impact on balance and patellofemoral kinematics. However, normal anatomic relationships between rotational axes are poorly understood. As such, we sought to characterize anatomic femoral rotational axes in patients undergoing primary TKA. METHODS: We identified 100 patients who underwent a primary TKA with a preoperative computed tomography scan. The angles between the surgical epicondylar axis (SEA) and the anterior-posterior (AP) axis to the posterior condylar axis (PCA) were measured independently by a musculoskeletal fellowship-trained radiologist and a fellowship-trained arthroplasty surgeon. We simulated an ideal TKA in which the femoral component was placed exactly 3° external to the PCA and measured resulting rotation. RESULTS: The SEA was on average 1.5° externally rotated to the PCA (range 3.1° internal to 7.0° external). The AP axis was on average 4.5° externally rotated to the PCA (range 2.3° internal to 10.3° external). The AP axis was a mean 2.7° externally rotated to the SEA (range 6.3° internal to 10.3° external). Routinely setting femoral rotation 3° external to the PCA would result in only 51 (51%) TKAs within ±2° of the SEA and 23 (23%) femoral components internally rotated relative to the SEA. CONCLUSION: Normal anatomic rotational axes of arthritic knees are highly variable, with a 10° range in the SEA and 16° range in the AP axis. Routinely setting femoral rotation 3° external to the PCA will yield significant error in aligning the femoral component with either the SEA or AP axis.

High Rate of Re-Revision in Patients Less Than 55 Years of Age Undergoing Aseptic Revision Total Knee Arthroplasty.

BACKGROUND: There are limited data on the outcomes of revision total knee arthroplasty in young patients. We sought to characterize the re-revision-free survival and risk factors for re-revision in patients less than 55 years who underwent aseptic revision TKA. METHODS: We retrospectively reviewed 197 revision TKAs at a mean follow-up of 5 years. Mean age was 49 years; mean body mass index was 31 kg/m2. Twenty-seven (14%) patients had at least 1 prior revision TKA. The most common indications for revision included instability (29%), arthrofibrosis (26%), and aseptic loosening (24%). Constraint included the following: 59 posterior-stabilized (30%), 123 varus-valgus constrained (62%), and 15 hinged (8%). Components revised included the following: 93 femur/tibia (47%), 68 polyethylene-only (35%), 19 femur-only (10%), and 17 other (9%). Survivorship free from re-revision was calculated via the Kaplan-Meier method and a multivariate Cox proportional regression was utilized to identify risk factors for re-revision. RESULTS: Survivorship free from any re-revision at 5 years was 80%. In the multivariate analysis, patients with a prior revision (hazard ratio [HR] = 2.78, P = .02), an isolated polyethylene exchange (HR = 3.0, P = .004), and a hinged prosthesis (HR = 3.47, P = .05) were significant risk factors for lower revision-free survival. Forty-two patients (21%) underwent re-revision, most commonly for periprosthetic joint infection (7%), instability (6%), and aseptic loosening (5%). Re-revision occurred in 18/68 (26%) patients undergoing an isolated polyethylene exchange. CONCLUSION: Patients less than 55 years undergoing revision TKA have a modest 5-year revision-free survival of 80%. Patients with prior revision TKAs (HR = 2.78), hinge type prostheses (HR = 3.47), and polyethylene-only revisions (HR = 3.0) had higher revision rates.

Total knee arthroplasty for patellofemoral arthritis.

BACKGROUND: Multiple treatment methods have been advocated for patellofemoral arthritis. The purpose of the present study was to report on our experience with the use of total joint replacement for the treatment of primarily severe patellofemoral arthritis of the knee in patients more than fifty-five years of age. METHODS: Between January 1980 and December 1994, thirty knee replacements were performed in twenty-seven patients for the treatment of arthritis that primarily involved the patellofemoral joint. The Ahlbück radiographic evaluation scale was used to grade the severity of arthritis; the mean score was 4.83 points (range, 4 to 5 points) for the patellofemoral compartment and 0.6 point (range, 0 to 1 point) for both the medial and lateral compartments. The patients included eighteen women and nine men who had a mean age of seventy-three years (range, fifty-nine to eighty-eight years). None of the patients had had any prior procedures on the knee, but all had been treated for a minimum of six months with nonoperative measures. The mean preoperative Knee Society score was 50 points (range, 20 to 64 points). RESULTS: At a mean duration of follow-up of eighty-one months (range, forty-eight to 133 months), there were twenty-eight excellent, one good, and one poor result. The mean Knee Society objective score was 93 points (range, 67 to 100 points). The poor result was in a patient who sustained a rupture of the patellar tendon postoperatively as the result of a fall, which necessitated a tendon reconstruction. CONCLUSION: Total knee arthroplasty was found to be a viable treatment option in patients more than fifty-five years of age with primarily severe patellofemoral disease.