Diagnosing Flexion Laxity after Knee Arthroplasty Using the "Hanging" Clunk Test and the Standard-to-Hanging Lateral Difference.

Abstract

Flexion laxity after total knee arthroplasty (TKA) may be difficult to diagnose. We describe simple clinical and radiographic tests that may aid in the identification of this problem. There were 99 consecutive non-selected patients who had 128 TKAs presenting to our clinic for scheduled or unscheduled follow-up at a minimum of one year post-procedure, who were enrolled in an Institutional Review approved study. Patients were divided into two groups (cases = self-report of pain, controls = no pain). All patients underwent routine clinical and radiographic evaluation, as well as physical examination for a hanging clunk sign, and one additional radiographic examination (hanging lateral radiograph). For the cases group (n = 51), a positive hanging clunk sign was identified in six patients. Clinical flexion laxity was identified in two patients. For the control group (n = 76), a positive hanging clunk sign was identified in 15 patients. Clinical flexion laxity was identified in three patients. At a standard-to-hanging lateral difference >= four mm, 11 patients complained of pain, and seven did not (61%, specificity: 91%, sensitivity: 23%, accuracy: 64%). The overall incidence of a positive hanging clunk sign was 16.5%. Isolated flexion laxity may be difficult to diagnose. Flexion laxity after total knee arthroplasty may be difficult to diagnose. The clinical complaint of pain correlated with a radiographic flexion gap difference of four mm or greater. The hanging lateral radiograph may assist in identifying isolated flexion laxity after TKA.