The value of valgus stress radiographs in the workup for medial unicompartmental arthritis

Abstract

Background: High tibial osteotomy and unicompartmental knee arthroplasty are surgical treatment options for unicompartmental knee arthritis; these procedures are indicated for patients who do not have severe arthritis in the lateral compartment. Valgus stress radiographs sometimes are used to make this evaluation, but this test has not been critically evaluated.

Questions/purposes: We sought to determine (1) whether valgus stress radiographs help to evaluate the integrity of the cartilage in the lateral compartment in patients undergoing TKA for noninflammatory arthritis, and (2) whether valgus stress radiographs can identify patients whose varus deformity is correctable.

Methods: We reviewed preoperative hip-to-ankle standing radiographs, AP standing radiographs, and valgus stress radiographs of 84 patients (91 knees) who underwent TKA for varus knee arthritis between July 2010 and January 2012. Valgus stress radiographs were obtained with the patient supine with the knee 20° flexed and a firm manual valgus force was applied through the knee. On valgus stress radiographs, the lateral compartment joint space width and the corrected mechanical alignment were measured. Intraoperative cartilage assessment (Outerbridge grade) was compared with lateral compartment joint space width. Knees with mechanical leg alignment of 3° varus to 3° valgus on valgus stress radiographs were considered correctable deformities.

Results: The lateral compartment joint space width on valgus stress radiographs did not correlate with the intraoperative Outerbridge grading of the lateral compartment cartilage (rs = -0.154; p = 0.146). The majority of knees (93%; 55 of 59) with 10° or less mechanical varus on hip-to-ankle standing radiographs were correctable within the range of 3° varus to 3° valgus.

Conclusions: Valgus stress radiographs provided no added benefit to the radiographic assessment of the lateral compartment cartilage and regarding the correctability of the varus deformity.

Fig. 1A–B

(A) A standardized left AP standing radiograph shows the knee of a 79-year-old woman with Kellgren-Lawrence Grade 3 osteoarthritis in the medial compartment and Grade 1 in the lateral compartment, respectively. (B) The corresponding valgus stress radiograph shows the measurements of the medial (5.7 mm) and lateral (5.4 mm) joint space width and the correctability of the varus deformity as an angle between axis a and b, respectively. Manual valgus force corrected the deformity to 1° varus.

Fig. 2

A scatterplot illustrates the relationship between lateral compartment joint space width on valgus stress radiographs and intraoperative cartilage assessment (Outerbridge grading scale) of the lateral compartment for the entire cohort (n = 91). All knees with an Outerbridge Grade of 0, 1, 2, or 3 maintained a joint space width of 4 mm or more.

Fig. 3

A scatterplot illustrates the relationship between the lateral compartment joint space width on valgus stress radiographs and Kellgren-Lawrence grades of the lateral compartment assessed on standing AP radiographs for the entire cohort (n = 91). All knees with a lateral Kellgren-Lawrence Grade 1 or 2 maintained a lateral joint space width of 4 mm or more on valgus stress radiographs. All knees with a lateral Kellgren-Lawrence Grade 4 had a lateral joint space width less than 4 mm.

Fig. 4

A scatterplot illustrates the relationship between the corrected mechanical alignment on valgus stress radiographs and the mechanical varus alignment (hip-knee-ankle angle) on hip-to-ankle radiographs for the entire cohort (n = 91). There is a significant correlation between the degree of correctability on the valgus stress radiograph and the mechanical alignment on the hip-to-ankle radiograph.