Specific examination-arthritis or joint surface damage
The hallmark signs when examining for joint surface damage are signs associated with higher friction, felt on moving one joint surface on its opposing surface under compression.
Crepitus on joint movement can be heard but it usually needs to be felt. Active movement loads the joint and the examiner places a hand over the moving part, either feeling with the fingers or the flat of the palm.
Popping, snapping or clunking may be felt on movement under load. The characteristic of these noises needs to be noted with specific reference to whether the sensations remind the patient of their symptoms. Many knees will make some form of noise on moving and painless noises are generally considered ‘safe’.
Bare Bone crepitus.
When two bare bone surfaces are forcibly compressed together then there is very high friction and the surfaces momentarily stick together before sliding in a juddering fashion. This sign has been described as the pepper mill sign for obvious analogous reasons. When the patient admits this is what happens when getting up from a chair or on stooping, giving them a feeling of not trusting the knee, then it confirms the extent of their osteoarthritis – even if subsequent x-rays still seem to show the presence of a gap between the surfaces.
It is worth remembering that on the medial compartment the worn surface is most at about 30 degrees flexion, in the lateral compartment wear is at slightly greater flexion. In the patello-femoral joint it is the lateral patella facet and trochlea groove that are most commonly affected.
Patello-femoral compartment: the patella is compressed into the groove and the knee gently rocked by flexing and extending at 10 – 30 degrees, or the patella is moved medially/laterally while compressing.
Medial compartment: the leg is brought into hip abduction, external rotation and 30 degrees knee flexion, resting the knee against the examiners hip for counter pressure. The patients foot is cupped in one hand and the flat palm of the examiners other hand is then used to both sense grating and to hold the knee against the examiners hip. Firm varus force is then applied to the knee and the joint slowly flexed. The key to this test is to allow the bony surfaces to ‘stick’ together by holding the knee still for 10 seconds or so before initiating very slow bending or straightening. What is happening is that the thin synovial fluid is being compressed out of the articulation removing any oily lubrication benefit.
Lateral compartment: to detect bare bone crepitus laterally the tibia is supported between the examiners elbow and side, while the opposite palm is placed against the lateral joint line with the knee bent at 450. Valgus force is applied and very slow flexion initiated trying to detect the surfaces catching.
Range of movement
Loss of range of movement, both flexion and extension is an early sign of joint degeneration. For consistency and accuracy it is best to measure flexion with the patient reclined nearly supine in order to avoid hip flexion, which may increase knee flexion.
Palpation of the joint surface with knee at 900
When the knee is at 900 the distal articular surface of the medial femoral condyle is facing distally and is not covered by the patella. Deep tenderness on palpation of this surface is consistent with articular surface damage.
Cysts and fullness in the popliteal fossa are best seen and palpated with the knee in extension and when standing.
History and examination are linked and specific examination is substantially determined by the likely diagnosis or group of diagnoses indicated by the history. That said it is important to undertake general examination of the knee taking into account appearance and examination with the patient, walking, standing, sitting and lying supine.
The various specific signs can be grouped together creating a pattern indicating a specific diagnosis.
Table 1: groups of diagnostic signs
Diagnosis or Disorder
Lachman test +, Pivot shift +
Reverse Lachmans test +, Posterior Draw +, Step off sign (grading)
Postero-lateral corner insufficiency
Prone Dial test +, Spin test +, Reverse pivot shift test +/-, Lateral knee thrust on walking
Knee arthritis (medial or lateral compartment)
Loss of range of movement, Bare bone crepitus.
Poor patella tracking, patella apprehension test +, increased patella glide
Medial meniscus tear
Effusion +, posteromedial joint line tenderness, McMurray test +, pain on squat walking
Lateral meniscus tear
Mid lateral joint line tenderness
Effusion, Pain on patello-femoral compression, crepitus felt on extending against gravity
Global anterior knee pain syndrome
Normal alignment tests, crepitus -, patella tendinopathy tests -.
Key Learning points:
- History and examination of the knee are linked and specific examination is determined by the likely diagnosis indicated by the history.
- The 5 diagnostics groups are: Anterior knee pain; Traumatic injury to knee ligaments, meniscus, or other structures; Degenerative osteoarthritis; Inflammatory joint problem; and other problems.
- General examination of the knee is still required with the patient, walking, standing, sitting and lying supine.