Hendrik A. Zuiderbaan

Why Do Medial Unicompartmental Knee Arthroplasties Fail Today

BACKGROUND Failure rates are higher in medial unicompartmental knee arthroplasty (UKA) than total knee arthroplasty. To improve these failure rates, it is important to understand why medial UKA fail. Because individual studies lack power to show failure modes, a systematic review was performed to assess medial UKA failure modes. Furthermore, we compared cohort studies with registry-based studies, early with midterm and late failures and fixed-bearing with mobile-bearing implants. METHODS Databases of PubMed, EMBASE, and Cochrane and annual registries were searched for medial UKA failures. Studies were included when they reported >25 failures or when they reported early (<5 years), midterm (5-10 years), or late failures (>10 years). RESULTS Thirty-seven cohort studies (4 level II studies and 33 level III studies) and 2 registry-based studies were included. A total of 3967 overall failures, 388 time-dependent failures, and 1305 implant design failures were identified. Aseptic loosening (36%) and osteoarthritis (OA) progression (20%) were the most common failure modes. Aseptic loosening (26%) was most common early failure mode, whereas OA progression was more commonly seen in midterm and late failures (38% and 40%, respectively). Polyethylene wear (12%) and instability (12%) were more common in fixed-bearing implants, whereas pain (14%) and bearing dislocation (11%) were more common in mobile-bearing implants. CONCLUSION This level III systematic review identified aseptic loosening and OA progression as the major failure modes. Aseptic loosening was the main failure mode in early years and mobile-bearing implants, whereas OA progression caused most failures in late years and fixed-bearing implants.

Medial unicompartmental knee arthroplasty improves congruence and restores joint space width of the lateral compartment

BACKGROUND Osteoarthritic progression of the lateral compartment remains a leading indication for medial unicompartmental knee arthroplasty (UKA) revision. Therefore, the purpose of this study was to evaluate the alterations of the lateral compartment congruence and joint space width (JSW) following medial UKA. METHODS Retrospectively, lateral compartment congruence and JSW were evaluated in 174 knees (74 females, 85 males, mean age 65.5years; SD±10.1) preoperatively and six weeks postoperatively, and compared to 41 healthy knees (26 men, 15 women, mean age 33.7years; SD±6.4). Congruence (CI) was calculated using validated software that evaluates the geometric relationship between surfaces and calculates a congruence index (CI). JSW was measured on three sides (inner, middle, outer) by subdividing the lateral compartment into four quarters. RESULTS The CI of the control group was 0.98 (SD±0.01). The preoperative CI was 0.88 (SD±0.01), which improved significantly to 0.93 (SD±0.03) postoperatively (p<0.001). In 82% of knees, CI improved after surgery, while in 18% it decreased. The preoperative significant JSW differences of the inner (p<0.001) and outer JSW (p<0.001) were absent postoperatively. CONCLUSION Our data suggests that a well-conducted medial UKA not only resurfaces the medial compartment but also improves congruence and restores the JSW of the lateral compartment.

ACL Fibers Near the Lateral Intercondylar Ridge Are the Most Load Bearing During Stability Examinations and Isometric Through Passive Flexion

Background: The femoral insertion of the anterior cruciate ligament (ACL) has direct and indirect fiber types located within the respective high (anterior) and low (posterior) regions of the femoral footprint. Hypothesis: The fibers in the high region of the ACL footprint carry more force and are more isometric than the fibers in the low region of the ACL footprint. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen cadaveric knees were mounted to a robotic manipulator. A 134-N anterior force at 30° and 90° of flexion and combined valgus (8 N·m) and internal (4 N·m) rotation torques at 15° of flexion were applied simulating tests of anterior and rotatory stability. The ACL was sectioned at the femoral footprint by detaching either the higher band of fibers neighboring the lateral intercondylar ridge in the region of the direct insertion or the posterior, crescent-shaped fibers in the region of the indirect insertion, followed by the remainder of the ACL. The kinematics of the ACL-intact knee was replayed, and the reduction in force due to each sectioned portion of insertion fibers was measured. Isometry was assessed at anteromedial, center, and posterolateral locations within the high and low regions of the femoral footprint. Results: With an anterior tibial force at 30° of flexion, the high fibers carried 83.9% of the total anterior ACL load compared with 16.1% in the low fibers (P < .001). The high fibers also carried more anterior force than the low fibers at 90° of flexion (95.2% vs 4.8%; P < .001). Under combined torques at 15° of flexion, the high fibers carried 84.2% of the anterior ACL force compared with 15.8% in the low fibers (P < .001). Virtual ACL fibers placed at the anteromedial portion of the high region of the femoral footprint were the most isometric, with a maximum length change of 3.9 ± 1.5 mm. Conclusion: ACL fibers located high within the femoral footprint bear more force during stability testing and are more isometric during flexion than low fibers. Clinical Relevance: It may be advantageous to create a “higher” femoral tunnel during ACL reconstruction at the lateral intercondylar ridge.

Annual revision rates of partial versus total knee arthroplasty: A comparative meta-analysis

BACKGROUND Utilization of unicompartmental knee arthroplasty (UKA) and patellofemoral arthroplasty (PFA) as alternatives to total knee arthroplasty (TKA) for unicompartmental knee osteoarthritis (OA) has increased. However, no single resource consolidates survivorship data between TKA and partial resurfacing options for each variant of unicompartmental OA. This meta-analysis compared survivorship between TKA and medial UKA (MUKA), lateral UKA (LUKA) and PFA using annual revision rate as a standardized metric. METHODS A systematic literature search was performed for studies quantifying TKA, MUKA, LUKA and/or PFA implant survivorship. Studies were classified by evidence level and assessed for bias using the MINORS and PEDro instruments. Annual revision rates were calculated for each arthroplasty procedure as percentages/observed component-year, based on a Poisson-normal model with random effects using the R-statistical software package. RESULTS One hundred and twenty-four studies (113 cohort and 11 registry-based studies) met inclusion/exclusion criteria, providing data for 374,934 arthroplasties and 14,991 revisions. The overall evidence level was low, with 96.7% of studies classified as level III-IV. Annual revision rates were lowest for TKA (0.49%, CI 0.41 to 0.58), followed by MUKA (1.07%, CI 0.87 to 1.31), LUKA (1.13%, CI 0.69 to 1.83) and PFA (1.75%, CI 1.19 to 2.57). No difference was detected between revision rates for MUKA and LUKA (p=0.222). CONCLUSIONS Revisions of MUKA, LUKA and PFA occur at an annual rate of 2.18, 2.31 and 3.57-fold that of TKA, respectively. These estimates may be used to inform clinical decision-making, guide patient expectations and evaluate the cost-effectiveness of total versus partial knee replacement in the setting of unicompartmental OA.

Notchplasty in anterior cruciate ligament reconstruction in the setting of passive anterior tibial subluxation

PURPOSE In an effort to minimize graft impingement among various ACL deficient states, we sought to quantitatively determine requirements for bone resection during notchplasty with respect to both volumetric amount and location. METHODS A validated method was used to evaluate Magnetic Resonance Imaging scans. We measured the ATT of the medial and lateral compartments in the following four states: intact ACL (27 patients), acute ACL disruption; <2 months post-injury (76 patients), chronic ACL disruption; 12 months post-injury (42 patients) and failed ACL reconstruction (75 patients). Subsequently, 11 cadaveric knees underwent Computed Tomography (CT) scanning. Specialized software allowed virtual anterior translation of the tibia according to the average ATT measured on MRI. Impingement volume was analyzed by performing virtual ACLRs onto the various associated CT scans. Location was analyzed by overlaying an on-screen protractor. The center of the notch was defined as 0°. RESULTS Average impingement volume changed significantly in the various groups compared to the intact ACL group (acute 577 ± 200 mm(3), chronic 615 ± 199 mm(3), failed ACLR 678 ± 210 mm(3), p=0.0001). The location of the required notchplasty of the distal femoral wall border did not change significantly. The proximal femoral border moved significantly towards the center of the notch (acute 8.6° ± 4.8°, chronic 7.8° ± 4.2° (p=0.013), failed ACLR 5.1° ± 5.9° (p=0.002)). CONCLUSION Our data suggests that attention should be paid peri-operatively to the required volume and location of notchplasty among the various ACL deficient states to minimize graft impingement.

Patients with isolated lateral osteoarthritis: Unicompartmental or total knee arthroplasty?

BACKGROUND Lateral unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are both reliable treatment options for patients with isolated lateral osteoarthritis (OA). However, studies comparing both procedures are scarce. Aims of this study were to (I) compare short-term functional outcomes following lateral UKA and TKA and (II) assess the role of patient characteristics on outcomes as measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). METHODS In this retrospective cohort study, 82 patients (48 undergoing lateral UKA and 34 undergoing TKA) were identified that presented with lateral OA and completed the WOMAC. Independent t-tests were used to compare outcomes following lateral UKA and TKA. RESULTS Mean follow-up was 2.8 years (range: 2.0 - 5.0 years). Preoperatively, no differences between lateral UKA and TKA were seen (50.1±13.5 and 53.3±17.1, respectively, p=0.551). Postoperatively, lateral UKA patients reported better overall outcomes than TKA (90.5±11.7 vs. 81.8±17.9, p=0.017). Subgroup analysis showed better outcomes following lateral UKA than TKA in patients younger than 75 years (92.1±9.9 vs. 81.3±19.6, p=0.014) and in females (91.6±9.9 vs. 81.0±18.2, p=0.014). CONCLUSION These findings indicate that lateral UKA has superior short-term functional outcomes compared to TKA in patients with isolated lateral OA. Better outcomes were especially seen in younger patients and females. These findings may help orthopedic surgeons choose treatment for patients presenting with lateral OA and optimize treatment for individual patients.

Medial Unicondylar Knee Arthroplasty Improves Patellofemoral Congruence: a Possible Mechanistic Explanation for Poor Association Between Patellofemoral Degeneration and Clinical Outcome

The purpose was to determine the effect of medial fixed bearing unicondylar knee arthroplasty (UKA) on postoperative patellofemoral joint (PFJ) congruence and analyze the relationship of preoperative PFJ degeneration on clinical outcome. We retrospectively reviewed 110 patients (113 knees) who underwent medial UKA. Radiographs were evaluated to ascertain PFJ degenerative changes and congruence. Clinical outcomes were assessed preoperatively and postoperatively. The postoperative absolute patellar congruence angle (10.05 ± 10.28) was significantly improved compared with the preoperative value (14.23 ± 11.22) (P = 0.0038). No correlation was found between preoperative PFJ congruence or degeneration severity, and WOMAC scores at two-year follow up. Pre-operative PFJ congruence and degenerative changes do not affect UKA clinical outcomes. This finding may be explained by the post-op PFJ congruence improvement.

Medial Subluxation of the Tibia After Anterior Cruciate Ligament Rupture as Revealed by Standing Radiographs and Comparison With a Cadaveric Model

Background: Biomechanical studies indicate that the tibia shifts medially and has a more valgus orientation in the anterior cruciate ligament (ACL)–deficient knee. However, it is not known whether these differences can be detected on standing radiographs. Purpose: To determine whether medial subluxation and more changes in coronal alignment of the tibia are detectable in both weightbearing radiographs and a cadaveric model simulating quiet standing. Study Design: Case series; Level of evidence, 4, and Descriptive laboratory study. Methods: Radiographic data were available for a cross-section of 74 patients with unilateral ACL tears. Tibial subluxation and coronal limb alignment were measured on hip-to-ankle weightbearing radiographs. Eight cadaveric knees were mounted on a 6 degree of freedom robot. Mediolateral position and varus-valgus alignment of the tibia relative to the femur were measured in response to 300-N axial compression simulating quiet standing at 5° and 15° of flexion with the ACL intact and sectioned. Results: Across all 74 patients included in the clinical study, the ACL-injured knee experienced 1.6 ± 2.3 mm (mean ± SD) of medial tibial subluxation compared with the contralateral uninjured knee (P < .001). The 24 patients with isolated ACL rupture exhibited 2.0 ± 1.8 mm of medial subluxation (P < .001). The mean coronal alignment of all 74 patients in the study was 0.7° ± 2.8° varus in the injured limb and 1.3° ± 2.6° varus in the uninjured contralateral limb (P = .0187). In the cadaveric model, the tibia translated 0.4 ± 0.5 mm more medially after sectioning of the ACL at 15° of flexion (P = .0485); however, no changes in coronal alignment were detected. Conclusion: The tibia shifts medially and is less varus in the ACL-deficient knee on standing radiographs. The medial tibial shift is reproduced in an axially loaded cadaveric model. Clinical Relevance: Medial tibiofemoral subluxation seen on frontal plane standing radiograph is an underappreciated sequela of isolated ACL rupture. The ability of ACL reconstruction to restore this aspect of ACL injury is not well understood and should be investigated further. Cadaveric models may be used to directly measure the mechanical effect of subtle changes in mediolateral position on articular contact stress as an indicator of the importance of this finding.

Coronal tibiofemoral subluxation: a new measurement method

BACKGROUND Coronal tibiofemoral (CTF) subluxation is a common finding in knee osteoarthritis (OA) which can be related to poor pain scores and tibial spine impingement. In this study we describe a new method for measuring CTF subluxation and present validation of the method using cadaveric knees. METHODS A prototype software code based on the ICP mathematical algorithm was developed to measure CTF subluxation; the code finds the rigid transformation that best aligns the articular surfaces, measures CTF subluxation and the angle between articular surfaces. For validation, three stripped fresh frozen cadaveric knee specimens were transfixed to a specially designed knee fixation device where tibiofemoral angle and CTF subluxation can be measured directly. Fluoroscopic images were obtained with the tibiofemoral joint in neutral alignment and with 5, 10 and 15 (mm) of medial and lateral subluxation. This procedure was repeated with a neutral tibiofemoral angle, 10° of varus and 10° of valgus. All images were analyzed independently by two investigators using the prototype software. RESULTS The interclass correlation coefficient between the two investigators for CTF subluxation and tibiofemoral angle was 0.93 and 0.99 respectively. The CTF subluxation and tibiofemoral angle measured by the software correlated to the CTF subluxation and tibiofemoral angle were defined using the knee fixation device, with Pearson product moments of 0.86 and 0.94 respectively. CONCLUSION Our suggested prototype software is precise, repeatable and reliable at measuring CTF subluxation and tibiofemoral angle. It may prove to be a useful tool to evaluate CTF subluxation in a clinical setting.

Passive Anterior Tibial Subluxation in the Setting of Anterior Cruciate Ligament Injuries: A Comparative Analysis of Ligament-Deficient States:

Background: Static anterior tibial subluxation after an anterior cruciate ligament (ACL) injury highlights the abnormal relationship between the tibia and femur in patients with ACL insufficiency, although causal factors including injuries to secondary stabilizers or the time from injury to reconstruction have not been examined. Purpose: To determine static relationships between the tibia and femur in patients with various states of ACL deficiency and to identify factors associated with anterior tibial subluxation. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Patients treated for ACL injuries were identified from an institutional registry and assigned to 1 of 4 cohorts: intact ACL, acute ACL disruption, chronic ACL disruption, and failed ACL reconstruction (ACLR). Anterior tibial subluxation of the medial and lateral compartments relative to the femoral condyles were measured on magnetic resonance imaging (MRI), and an MRI evaluation for meniscal tears, chondral defects, and injuries to the anterolateral ligament (ALL) was performed. Results: One hundred eighty-six ACL-insufficient knees met inclusion criteria, with 26 patients without an ACL injury utilized as a control group. In the lateral compartment, the mean anterior tibial subluxation measured 0.78 mm for the control group (n = 26), 2.81 mm for the acute ACL injury group (n = 74), 3.64 mm for the chronic ACL injury group (n = 40), and 4.91 mm for the failed ACLR group (n = 72). In the failed ACLR group, 37.5% of patients demonstrated lateral compartment anterior subluxation ≥6 mm, and 11.1% of this group had anterior subluxation of the lateral compartment ≥10 mm. Multivariate regression revealed that the presence of both medial and lateral chondral defects was associated with a mean 1.09-mm increase in subluxation of the medial compartment (P = .013). The combination of medial and lateral meniscal tears was an independent predictor of increased lateral tibia subluxation by 1.611 mm (P = .0022). Additionally, across all knee states, an injury to the ALL was associated with increased anterior tibial subluxation in both the medial compartment (P = .0438) and lateral compartment (P = .0046). In 29.4% of knees with ALL injuries, lateral tibial subluxation was ≥6 mm, but with multivariate regression analysis, an ALL injury was not an independent predictor of anterior subluxation of the lateral compartment. Conclusion: Knees with failed ACLR are associated with more anterior tibial subluxation than those with primary ACL deficiency. Using previously reported thresholds of 6 to 10 mm of lateral compartment subluxation for a positive pivot shift, between 11.1% and 37.5% of knees with failed ACLR may be in a “resting pivoted position.” In primary ACL-deficient knees, anterior tibial subluxation is associated with chondral injuries and meniscal tears but not injury chronicity.