GP tips on assessing hip and knee conditions — a practical guide

GPs are the frontline for the vast majority of hip and knee presentations. Getting the assessment right from the start — knowing what to look for, which tests to do, and when imaging is genuinely useful — makes a real difference to how quickly a patient gets the right care. This guide outlines a practical approach to hip and knee assessment in general practice, written from the perspective of what I find most useful when patients arrive in the orthopaedic rooms.

Hip assessment

Start with the red flags. Before anything else, screen for features that would take the assessment in a different direction entirely. Night pain that wakes the patient, constitutional symptoms such as fever, night sweats, or unexplained weight loss, and an elevated inflammatory markers should raise concern about malignancy or septic arthritis. These patients need urgent investigation, not a wait-and-see approach.

Observe the gait. Watching a patient walk from the waiting room to the consulting room gives more information than most people realise. An antalgic gait (short stance phase on the painful side) is non-specific but tells you the pain is significant. A Trendelenburg gait — the pelvis dropping on the swing side with each step — points to abductor weakness, which can be seen in advanced hip OA or in gluteal pathology.

Range of motion. With the patient supine, assess hip flexion, internal rotation, and external rotation. The single most reliable early finding in hip osteoarthritis is loss of internal rotation. Patients often present with a reasonable range of flexion but noticeably restricted and painful internal rotation well before plain XR shows significant change. This is worth examining even if the patient has not specifically complained of hip pain — groin, thigh, and even knee pain can all be referred from the hip.

FADIR and FABER tests. FADIR (Flexion, Adduction, Internal Rotation) is positive in femoroacetabular impingement (FAI) and labral pathology — it reproduces anterior groin pain by loading the anterior joint. FABER (Flexion, Abduction, External Rotation) tests the sacroiliac joint as well as the hip; pain in the groin with this test is more suggestive of hip pathology, while pain in the posterior pelvis suggests SI joint involvement.

Hip vs lumbar spine. Groin pain with a restricted, painful hip ROM on examination almost always originates from the hip. Buttock and posterior thigh pain is less discriminating and can come from both the hip and the lumbar spine. The key distinguishing feature: pain that is reproduced by hip rotation in extension (the log roll test) is more likely to be hip-derived. Pain that is unchanged by hip ROM and is accompanied by neurological symptoms (paraesthesia, weakness, dermatomal distribution) points to the spine.

Knee assessment

Inspect and palpate first. Look for swelling, deformity (varus or valgus), and muscle wasting (particularly VMO). Palpate for an effusion using the patella tap or the bulge sign. A significant effusion is always pathological and warrants investigation — it can represent haemarthrosis (acute trauma, often ACL or meniscal), synovitis (inflammatory arthritis), or infection.

ACL testing. The Lachman test — performed with the knee at approximately 20 to 30 degrees of flexion, assessing anterior tibial translation relative to the femur — is the most sensitive clinical test for ACL integrity. The anterior drawer test (knee at 90 degrees) is less sensitive in the acute setting due to muscle guarding. A positive Lachman with a soft or absent endpoint is highly suggestive of ACL disruption.

Meniscal assessment. Joint line tenderness — medial or lateral — is the most reliable clinical sign of meniscal pathology. McMurray's test (rotational stress with the knee moving from flexion to extension) and the Thessaly test (standing on one leg at 20 degrees of flexion, rotating the body) can add supporting information. Neither test is perfectly sensitive, so clinical suspicion based on history and joint line tenderness remains most important.

Collateral ligaments. Apply valgus stress at 0 degrees and 30 degrees of flexion to test the medial collateral ligament. Apply varus stress in the same positions for the lateral collateral ligament. Laxity at 30 degrees with tightness at 0 degrees suggests an isolated collateral injury. Laxity at both positions suggests a more complex multi-ligament injury and warrants prompt specialist review.

Patellofemoral joint. The patellar grind test (compressing the patella against the trochlea while asking the patient to contract the quadriceps) and the apprehension test (laterally displacing the patella while watching for the patient's reaction) assess patellofemoral pathology. Pes anserine tenderness — on the medial tibia approximately four to five centimetres below the joint line — is a common and underdiagnosed cause of medial knee pain that can mimic meniscal or OA-related pain.

Imaging guidance

Start with plain X-rays. Weight-bearing X-rays are essential for assessing joint space, and bilateral views allow direct comparison. For the hip, an AP pelvis is standard; a lateral view (frog-leg or cross-table) adds information about the femoral head and neck. For the knee, a bilateral standing AP, lateral, and skyline (patellofemoral) view is a useful routine set. Non-weight-bearing X-rays of the knee significantly underestimate joint space loss in OA — always specify weight-bearing.

MRI for soft tissue pathology. MRI is the appropriate next investigation for suspected meniscal tears, ACL injury, labral tears, or cartilage pathology. It adds genuine value in these situations. Where MRI is less useful — and where it is overused — is in older patients with established or suspected OA. In this group, MRI frequently generates incidental findings (meniscal degeneration, cyst formation, bone marrow oedema) that do not change management and can create unhelpful anxiety. If the clinical picture is consistent with OA in an older patient, weight-bearing X-rays are usually sufficient.

CT scanning is primarily a pre-surgical planning tool — it provides detailed three-dimensional bony anatomy useful for complex cases, revision surgery, and robotic-assisted procedures. It is rarely needed in the initial assessment of a new hip or knee presentation.

Earlier referral is almost always better than later. Waiting until end-stage disease reduces surgical options and makes rehabilitation harder.

When to refer

For osteoarthritis of the hip or knee, the common mistake is to wait too long. Patients often present having managed symptoms for years and arrive with severe disease, significant deconditioning, and sometimes a BMI that substantially increases surgical risk. Referring earlier — even if surgery is not immediately on the table — allows a proper discussion of non-surgical management, appropriate expectations, and surgical planning when the time comes. Most orthopaedic surgeons are happy to see patients well before they are at the point of surgery.

For soft tissue injuries — ACL tears, significant meniscal tears, and multi-ligament injuries in active patients — prompt referral is appropriate. In young athletes particularly, delayed diagnosis and delayed management carry real risks to long-term knee function. Do not wait for XR changes; if the clinical picture and MRI are consistent with significant pathology, refer early.

Any suspicion of septic arthritis, periprosthetic infection, or pathological fracture should prompt urgent referral or emergency department attendance, not a routine appointment.

What to include in a referral

A useful referral letter includes: a concise clinical history; the relevant examination findings (ROM, positive tests); imaging already performed, with the disc or images attached or forwarded; the patient's functional limitations (what they can and cannot do); BMI and relevant comorbidities; and — importantly — what the patient is hoping for from the consultation. A patient referred "for hip pain" is very different from one referred "for progressive left hip OA affecting her work as a nurse, who is keen to discuss surgical options."

For further information on referrals, preferred imaging, and what to include, visit the For GPs page on this website.