Kneeling Stress Radiography a forgotten yet dependable tool for Posterolateral Knee Instability

Diagnosing postero-lateral knee instability is a challenge from both clinical and radiologic perspective and can lead to significant morbidity if left untreated. Delayed diagnosis leads to a more demanding surgery and prolonged rehabilitation for the patient.

Stress radiography (SR) lost its popularity in recent years due to more dependence on instrumented laxity measurement (KT-1000) along with MRI. Kneeling stress radiograph is a lost art but remains invaluable in the assessment of posterolateral knee instability.

Quamar Azam et al conducted a prospective observational study to re-explore the undeniable utility of this forgotten tool in early diagnosis of posterolateral knee instability and identifying the mean posterior tibial translation distance (PTTD) and also assessing side to side difference (SSD) between the injured and the contralateral normal knee.

All patients with suspected ligament injuries were clinically evaluated using Lachman test, Drawer test (included palpation of tibial step of and posterior sag test, Godfrey test), Pivot shift test, Dial test (at 30° and 90° in the prone position and more than 10° of difference in external rotation from the normal side was considered significant), and Varus-valgus stress tests (at zero and 30°).

KSR (kneeling stress radiograph) was employed as a routine additional tool besides clinical examination and routine 3 T MRI. Patients were made to stand on one leg while the knee to be examined was flexed to 90° and kept on well-padded but firm support. The thigh was placed perpendicular to the horizontal leg and the patient was asked to rotate approximately 10° towards the examination side to superimpose the femoral condyles. The knee must be as close as possible to the film and the X-ray beam should be perpendicular to the film. Just before acquisition, the patient was asked to bear complete (or near-complete) weight on the knee under examination while the contralateral leg (on the ground) provides proprioception for required balance.

The observations of the study were:

• Total 27 patients were included in the study, with males being 4.4 times more commonly injured as compared to females.

• The most common mode of injury was motor vehicle accident (MVA).

• Out of 27 patients, 11 had isolated PCL (posterior cruciate ligament) injury while the rest had PLC (posterolateral corner) involvement.

• The mean SSD of PTTD was 8.79 mm in patient with isolated PCL. This was increased by 1.65 times (14.52 mm) in patients with co-existing PLC involvement.

The authors commented that – "The three main points to remember include—perpendicular position of knee relative to thigh, both femoral condyles should superimpose, and maximal weight should be born on the knee under examination."

The authors concluded that - Stress radiography is an indelible tool and serves as an adjunct to MRI imaging. It is not a substitute for clinical assessment but assists in early diagnosis and management, facilitating surgical planning and furnishing objective evidence of PCL/PLC functionality which is not possible with any other imaging modality.

Further reading:

Kneeling Stress Radiography: A Forgotten yet Dependable Tool for Postero lateral Knee Instability

Quamar Azam, Abhishek Chandra et al

Indian Journal of Orthopaedics (2022) 56:1729–1736

https://doi.org/10.1007/s43465-022-00721-5