Osteoporosis affects component positioning in computer navigation-assisted total knee arthroplasty.

Although computer-assisted navigation in total knee arthroplasty (TKA) has many advantages, undetected tracker pin movement can result in poor lower limb alignment and component position. Osteoporosis may be an underlying cause of tracker pin movement. The present prospective case-control study compared 6-month radiographic outcomes in 44 osteoporotic and 56 non-osteoporotic knees undergoing navigation TKAs. Osteoporotic knees were defined as those having a T-score of -2.5 or less either in the femoral neck or lumbar spine or both. At postoperative 6 months' follow-up, the average coronal tibial component position was greater valgus in osteoporotic group than in nonosteoporotic group (non-osteoporotic=varus 0.7°±1.8°; osteoporotic=valgus 1.2°±3.4°; p=0.041). Multiple linear regression analysis showed that being in the osteoporotic group was a predictor of tibial coronal component position (ß=0.321, p=0.039). In addition, preoperative lumbar spine bone mineral density was found to be a predictor of coronal and sagittal alignments of the tibial component (ß=0.406, p=0.015, ß=-0.463, p=0.007). The present study found that osteoporosis affected tibial component position in computer-assisted navigation TKA. Clinicians should be particularly aware of the possibility of undetectable tracker pin movement during navigation TKA in osteoporotic knees.

The impact of a rectangular or trapezoidal flexion gap on the femoral component rotation in TKA.

PURPOSE: The influence of soft tissue balancing on femoral component rotation in the gap technique remains unclear. The present study therefore compared the reliability of femoral component rotation determined by rectangular and trapezoidal gaps in total knee arthroplasty (TKA) using a navigation-assisted gap-balancing technique. The study also determined the correlation between femoral component rotation and gap measurement. METHODS: This prospective study included 99 patients (108 knees) who underwent postoperative CT after TKA with the navigation-assisted gap-balancing technique. A trapezoidal flexion or extension gap was defined as a >3 mm difference between the medial and lateral sides in 90° flexion or extension. An outlier of femoral component rotation was defined as >3° deviation from the transepicondylar axis. RESULTS: Postoperative CT showed that the femoral component had a tendency to rotate externally, with a mean 1.88 ± 2.49° from the surgical transepicondylar axis. Outliers and mean values of femoral component rotation were similar in the trapezoidal and rectangular flexion/extension gap groups. The medial flexion gap (r = -0.49, P = 0.007) and flexion gap differences (r = -0.59, P = 0.027) showed statistically significant negative correlations with the femoral component rotation. Multiple linear regression analysis also showed that the femoral component rotation was independently related to the flexion gap difference (ß = -0.27, P = 0.031). CONCLUSION: In the gap technique, the rotation of the femoral component is affected more by the flexion gap than by the extension gap. However, neither the trapezoidal nor rectangular flexion gap influenced femoral component rotation.

Shed blood re-transfusion provides no benefit in computer-assisted primary total knee arthroplasty.

PURPOSE: This matched case-cohort retrospective study examined the effectiveness of shed blood re-transfusion in reducing the need for allogeneic blood transfusion in computer-assisted primary cemented total knee arthroplasty (TKA). METHODS: The shed blood re-transfusion system used was the cell saver system. Data from 146 cases were analyzed (73 patients with cell saver, 73 patients without cell saver). RESULTS: The ABT rate was similar in each group. The mean allogenic blood transfusion volume was similar for each group (CS=214±453 ml, non-CS=288±447 ml). The only factors correlated with allogenic blood transfusion use were low preoperative hemoglobin and low body mass index. Two patients in cell saver group experienced shivering after re-transfusion. CONCLUSION: Shed blood re-transfusion provided no blood management benefits in computer-assisted primary TKA and is therefore recommended only for selected patients with low hemoglobin levels and low body mass index.

Accuracy of soft tissue balancing in TKA: comparison between navigation-assisted gap balancing and conventional measured resection.

Equalized rectangular extension and flexion gaps are considered desirable to ensure proper kinematics in total knee arthroplasty (TKA). We compared soft tissue balancing in TKAs performed using navigation-assisted gap-balancing (60 knees) and conventional measured resection (56 knees). The outlier of soft tissue balancing was defined as a gap difference >3 mm between the medial and lateral sides in 90 degrees flexion and extension. Medial or lateral outliers in extension or flexion were observed in 12% (7 of 60) navigation TKAs and 25% (14 of 56) conventional TKAs (p = 0.028). There were more outliers in flexion-extension gap difference on the medial side in the conventional (23%) than in the navigation-assisted (5%) group (p = 0.025). However, the proportion of flexion gap difference, extension gap difference, and lateral gap difference outliers did not differ significantly between the two groups (n.s.). Additionally, clinicoradiologic outcomes were similar for the two groups except for the postoperative mechanical axis outlier (p = 0.012). Navigation-assisted soft tissue balancing in TKA reduced not only the postoperative alignment outlier, but also the medial gap difference and achieved a more rectangular flexion and extension gap compared with conventional TKA.

Femoroacetabular impingement due to synovial chondromatosis of the hip joint.

This article describes a rare case of primary synovial chondromatosis of the hip associated with classical femoroacetabular impingement. A 38-year-old man presented with left hip pain of 3 years' duration and range of motion (ROM) limitations. Flexion abduction external rotation and impingement tests were positive and preoperative Harris Hip Score was 68. Radiographs showed multiple loose bodies, a calcified labrum, and a bump at the head-neck junction. Computed tomography (CT) confirmed the findings. Acetabular overcoverage and the crossing over sign were present. The lateral center edge angle was 48 degrees, acetabular roof angle was +2 degrees, alpha angle was 80 degrees, triangular index was 2 mm more than the radius of the femoral head, and anterior offset was 4.5 mm. Magnetic resonance imaging (MRI) revealed an acetabular labral tear, impaction on the femoral head-neck junction, and mild synovial hypertrophy with no acetabular cartilage damage. Loose body removal along with a total synovectomy, excision of the calcified labrum, and osteochondroplasty of the head-neck junction were performed after safe surgical dislocation. At 6-month follow-up, the patient was doing well with a Harris Hip Score of 96, improved ROM, and negative flexion abduction external rotation and impingement tests. Early diagnosis of synovial chondromatosis and impingement can be made by MRI and CT. Clinically, flexion abduction external rotation and impingement tests are positive in 99% and 97% of cases, respectively. Although arthroscopy management has been described for both the entities separately, it has drawbacks. With an open procedure, debridement of the hip joint and excision of femoral and acetabular impingement deformities are possible at the same time.