Risk factors of postoperative valgus malalignment in mobile-bearing medial unicompartmental knee arthroplasty.

OBJECTIVE: The aim of this observational study was to investigate the risk factors of postoperative valgus malalignment after mobile-bearing medial unicompartmental knee arthroplasty (UKA). METHODS: We retrospectively evaluated radiographic and surgical characteristics in 122 consecutive Oxford phase 3 UKAs. According to postoperative hip-knee-ankle angle (HKAA), 24 knees were sorted into group valgus with HKAA > 180° and 98 knees were sorted into group non-valgus with HKAA ≤ 180°. Logistic regression was performed to analyze risk factors including age, gender, BMI, side, preoperative limb alignment HKAA, preoperative LDFA, MPTA, FTFA, thickness of polyethylene bearing insert, tibial prothesis size, femoral prothesis size, medial tibial cut thickness, thickness of distal femoral mill, prothesis angle of coronal, and sagittal plane. RESULTS: The mean mechanical preoperative HKAA of 174.39°±4.23° was corrected to 178.18°±3.49° postoperatively (t = - 13.45, p = 0.000). The mean of postoperative HKAA in valgus group and non-valgus group was 183.45 ± 2.21° and 176.88 ± 2.35°, respectively (t = 12.44, p = 0.000). After statistical analysis with univariate analysis, eight risk factor variables among 16 independent variables were identified as potential predictors with p value ≤ 0.1. Multivariate logistic regression analysis for these eight potential predictors revealed that tibial cut (p = 0.046), LDFA (p = 0.003), MPTA (p = 0.011), and FTFA (p = 0.008) were significant risk factors predicting postoperative valgus malalignment after mobile-bearing UKA. CONCLUSIONS: Preoperative smaller LDFA, FTFA, larger MPTA and less medial tibial cut thickness were significantly associated with postoperative valgus malalignment in mobile-bearing UKA.

The efficacy and complications of 2-hole 3.5 mm reconstruction plates and 4 mm noncanulated cancellous screws for temporary hemiepiphysiodesis around the knee.

BACKGROUND: Persistent angular deformities around the knee can lead to growth-plate damage in childhood and osteoarthritis in adulthood. The treatment options include osteotomy and hemiepiphysiodesis. Tension-band plate hemiepiphysiodesis with 8-plate is an effective way to correct these deformities. However, its high cost makes it less available in many countries. In the present series, we have used 3.5 mm reconstruction plates for tension-band temporary hemiepiphysiodesis. METHODS: Twenty-one patients with bilateral angular deformities of the knee (42 extremities) underwent temporary hemiepiphysiodesis with 3.5 mm reconstruction plates. The diagnosis, BMI, weight, amount of correction of the deformity age, and device failure were analyzed. The mean follow-up period after plate removal was 17 months (ranging from 8 to 24 mo). RESULTS: The mean age of the patients was 10 years and 3 months (± 2 y and 10 mo). Complete correction of the deformities was achieved in 86% of patients. Of the 58 plate and screw constructs, 10% had screw breakage. Patients with genu valgum had 2 screw failures (6.25%), but in the genu varum group there were 4 screw failures (40%). Of the 3 patients who did not have complete correction of the deformities, 2 had mucopolysaccharidosis and 1 was nearing skeletal maturity (16 y old). The age of the patient, body weight, BMI, and degrees of angulation did not have any statistically significant correlation with the screw failure. Screw failures in female patients were more common than in male patients. All implant failures occurred in idiopathic patients. CONCLUSIONS: The efficacy of 3.5 mm reconstruction plates for temporary hemiepiphysiodesis around the knee is similar to that of 8-plates. However, the reconstruction plates have a lower cost and are easily available. Noncanulated 3.5 or 4.5 mm cortical screws seem to be superior to 4 mm noncanulated cancellous screws. LEVEL OF EVIDENCE: Level 3.