Arthroplasty in the Valgus Knee: Comparison and Discussion of Lateral vs Medial Parapatellar Approaches and Implant Selection

Constrained implants are frequently used for primary total knee arthroplasty (TKA) in patients with moderate and severe genu-valgum (>10˚). This deformity presents corrective challenges for ligament release. The lateral-parapatellar approach has been advocated as an alternative to the traditional medial-parapatellar approach. Claimed advantages include better access for release of tight ligamentous structures, without requirement for release of the medial-collateral ligament. We present our comparative experience of the use of an unconstrained knee-replacement prosthesis inserted by the lateral-parapatellar approach in comparison to a constrained-knee prosthesis inserted via the medial-parapatellar approach. 49 primary total knee-replacements in 48 (6 males, 42 females) patients were performed; 32 through a lateral-parapatellar approach (group L) using an unconstrained-prosthesis and 17 through a medial-parapatellar approach more often requiring a constrained-prosthesis (group M). Mean preoperative valgus angle was 18.5 (range 11-34˚). Patient demographics (p=0.7) and valgus correctability were similar between the two groups. There was no significant difference in the mean post-operative valgus angle. This was 4.2˚ (range 1-9.5˚) using the lateral-parapatellar approach and 5.3˚ (range 0.3-10˚), p=0.12, using the medial-parapatellar approach. Transient common peroneal injury occurred in 2 patients, both group L, in the presence of valgus angles of greater than 20˚. To date no joints have been revised, or are unstable. The use of a lateral-parapatellar approach, appropriate soft tissue release, and an unconstrained PCL-preserving implant, yielded in all cases a stable, well aligned knee arthroplasty. This represents a viable alternative to the constrained-prosthesis using a medial-parapatellar approach in patients with moderate and severe genu-valgum.

Non-steroidal hip arthropathy: case histories and differential diagnosis

A 74-year-old male patient was admitted for elective hip replacement surgery. X-rays revealed dramatic collapse and deformity of the femoral head over a 13-month period (Figures 1 and 2). He had experienced progressive hip discomfort during an 18-month period before surgery and was taking diclofenac (50 mg three times a day) regularly for discomfort. Despite analgesia, his walking distance had deteriorated from 800 to 100 metres while awaiting surgery.

Femoral head measurement in hemiarthroplasty: assessment of interobserver error using 3 measuring systems

We have assessed the consistency of measurement of femoral head circumference using 3 standard measuring instruments used in hemiarthroplasty of the hip. Fifty femoral heads were independently sized by ten independent observers using a caliper, a half circular measuring template, each allowing measurement to the nearest millimeter. We found significantly greater variance of the results using the half-circular templates (p=0.001) and the calipers (p=0. 011) compared with the full circular measuring templates. Measurement with calipers underestimated femoral head size by 0.72 mm compared with full circular measuring templates (p=0.02). Insertion of an undersized hemiarthroplasty head is a cause of increased point loading of the acetabulum and may result in increased rates of acetabular erosion. The use of full circular measurement templates is recommended as the most consistent method for head sizing in hemiarthroplasty of the hip.