What the pelvic drop actually means

A limp that lingers long after the wound has healed is one of the more frustrating experiences patients report after hip replacement. The hip feels broadly comfortable, yet walking still looks and feels uneven — and no amount of rest seems to resolve it. In many cases, the underlying pattern is Trendelenburg gait: a drop of the pelvis on the side opposite the operated hip during each step, as the leg on the operated side briefly carries full body weight.

First described by Friedrich Trendelenburg in 1895, the pattern arises when the gluteus medius and gluteus minimus muscles on the operated side cannot hold the pelvis level during single-leg support. The result is a characteristic lateral lean toward the operated side mid-stride — a movement that looks like a rolling limp and is often mistaken for simple post-operative soreness.

It is far from rare. A 3D motion-capture study of 89 patients found Trendelenburg gait in approximately 27% of total hip arthroplasty (THA) cases at a mean of 1.3 years post-operatively — meaning roughly one in four people are still affected well beyond the initial recovery window.

Recent inertial sensor research adds a detail that matters for rehabilitation: in 90% of severe Trendelenburg cases, the dominant pelvic movement is a shift contralateral to the affected side, not ipsilateral as older textbooks suggested. This distinction shapes how clinicians and patients should interpret — and correct — what they observe during walking.

Left unaddressed, the pattern is not merely cosmetic. Repeated asymmetric pelvic drop alters load transfer across the new joint, increases muscular fatigue, and tends to entrench compensatory movement habits throughout the lower limb and spine that become progressively harder to unwind.

The muscles responsible — and how they fail

Two muscle groups share responsibility for pelvic control during walking, and both can break down after hip arthroplasty in distinct ways.

The gluteus medius and gluteus minimus attach from the outer surface of the ilium down to the greater trochanter of the femur. During single-leg stance — the phase when the opposite foot is off the ground — these muscles contract to hold the pelvis level against gravity. When they are too weak or inhibited to maintain that resistance, the unsupported side of the pelvis drops: the classic Trendelenburg sign.

What 3D motion-capture research published in 2024 clarifies, however, is that the failure is not a single deficit but two co-occurring ones. In THA patients with Trendelenburg gait, hip abductor muscles show reduced eccentric contraction — that is, they fail to generate adequate force while lengthening under load during early stance. Simultaneously, the hip extensor muscles show reduced concentric contraction — they fail to generate propulsive force as they shorten through mid-stance. Neither failure alone fully explains the pattern; both operate together.

This matters because rehabilitation programmes that focus exclusively on abductor strengthening will leave the extensor deficit untreated. The extensors — principally gluteus maximus — contribute to the trunk control and forward momentum that allow the abductors to work efficiently; weakness in one group amplifies demand on the other.

A third contributor is increasingly recognised but frequently overlooked: the superior gluteal nerve (SGN), which innervates both gluteus medius and minimus. Ultrasound assessment of early post-THA patients consistently identifies tenderness in the tissue plane between these two muscles, implicating SGN entrapment or traction injury rather than isolated muscular atrophy. Where nerve involvement is present, purely load-based exercise may be insufficient without addressing the neural component directly.

How hip replacement surgery creates the weakness

Four distinct surgical factors can create or amplify abductor weakness after hip arthroplasty — and they operate independently of how much effort a patient puts into physiotherapy.

Approach-related tissue damage. Both posterior and lateral approaches require dissection near the gluteus medius, gluteus minimus, and the superior gluteal nerve that innervates them. Direct trauma or traction during this dissection can reduce muscle bulk and impair the eccentric contraction capacity that is the primary driver of pelvic control during mid-stance.

Greater trochanteric fracture. The abductor muscles attach directly onto the greater trochanter. Intraoperative fracture, or failure of the trochanter to unite postoperatively, removes a stable anchor for those muscles regardless of their baseline strength.

Leg-length discrepancy (LLD). LLD occurs in 3–30% of THA cases, with mean discrepancies of 3–17 mm. Even modest asymmetry persistently tilts the pelvis and loads the abductors unevenly on every step — a structural disadvantage that exercise alone cannot fully overcome.

Femoroacetabular offset. Restoring the hip's global offset to within ±2.5 mm of the native anatomy is associated with the best functional outcomes; approximately 90% of manually placed implants miss this target. Inadequate offset reduces the abductor moment arm — the geometric leverage the muscle requires to hold the pelvis level — directly amplifying Trendelenburg risk.

These four categories explain why surgical planning decisions have a direct bearing on rehabilitation trajectory. The SPAIRE technique addresses part of this problem at source: by preserving the piriformis and obturator internus tendons rather than dividing them, it retains two measurable features absent in conventional posterior surgery. The intact obturator internus creates a physical 'strap effect' across the posterior femoral head, and the preserved tendons retain their Golgi tendon organs and muscle spindles, sustaining the proprioceptive feedback that supports early neuromuscular re-engagement of the abductors. Large head-to-head gait-analysis trials comparing SPAIRE directly with standard posterior and anterior approaches have not yet been published, so the extent to which this soft-tissue preservation translates into a lower measured incidence of Trendelenburg gait remains unquantified — but the structural mechanism is substantive rather than theoretical.

Assessing how severe the Trendelenburg sign is

The standard clinical screening test remains the Trendelenburg sign: the patient stands on the operated leg for 30 seconds while the clinician observes the contralateral pelvis. A drop of more than a few degrees constitutes a positive result — but the degree of drop indicates where rehabilitation needs to begin.

Mild presentations show pelvic drop without trunk deviation. Moderate cases involve a visible lean towards the stance leg, a compensatory strategy that reduces moment-arm demand on the abductors but conceals the underlying weakness. Severe presentations produce a pronounced lateral list with compensatory arm swing, placing asymmetric load on the lumbar spine and contralateral hip with every step.

Single-leg stance testing confirms whether a problem is present; it cannot quantify its magnitude or detect subtle week-to-week change. Inertial sensor analysis and 3D motion-capture studies can measure pelvic obliquity, gait symmetry indices, and walking speed with a precision that clinical observation cannot match — and as noted earlier in this article, severe cases predominantly show contralateral rather than ipsilateral pelvic shift, a pattern that visual assessment tends to misread. Objective gait analysis platforms, including the MAI Motion® system used at MSK Doctors clinics, capture these biomechanical markers non-invasively, making it possible to document abductor recovery trajectory and set measurable milestones after hip arthroplasty.

Progress is best judged against functional criteria rather than weeks elapsed: resolution of the Trendelenburg sign on single-leg stance, symmetrical hip abductor strength measured by handheld dynamometry, sustained single-leg balance for 30 seconds, and walking speed returning towards age-matched norms. These are the markers that define genuine recovery.

Exercises that target the right muscles in the right way

Given those two distinct contraction failures, the exercise programme needs two parallel tracks rather than a single abductor routine.

Lateral band walks and monster walks are the evidence-supported starting point. Performed with a resistance band at the ankles or forefeet in a semi-squat posture, they produce moderate-to-high activation of both the gluteus medius and gluteus maximus while minimising tensor fasciae latae compensation — important when true abductor capacity is still limited and the TFL is ready to take over. The semi-squat position preloads the glutes and reduces the TFL's mechanical advantage, making these exercises mechanically appropriate for post-THA abductor re-education where selective recruitment, not simply leg movement, is the goal. Elevated and prolonged gluteus medius activation is the confirmed protective mechanism against Trendelenburg following lateral approach THA, which establishes the physiological target these exercises are designed to recreate.

Critically, the eccentric phase must be explicitly programmed. Controlling pelvic level on the return step — resisting gravity rather than only pushing outward against the band — is where the primary deficit lives. Concentric-only repetitions will not address it. A slow, loaded return phase is what distinguishes rehabilitation that targets the actual impairment from one that merely conditions the leg.

The second track runs in parallel: hip extensor loading. Glute bridges, progressing to single-leg variants as stability allows, address the concurrent concentric extensor failure that contributes to Trendelenburg at mid-stance. Neither track is optional.

SGN-targeted physiotherapy is a promising adjunct for early post-operative patients. In a case series of eight anterolateral-approach patients at 14 days post-THA, one session of ultrasound-guided superior gluteal nerve manual therapy combined with visual-feedback gluteus medius and minimus exercises improved hip abductor strength from 3.4 to 5.3 kgf, gait speed from 0.55 to 0.73 m/s, and walking pain from 3.6 to 1.5 on the NRS. These are clinically meaningful gains. The evidence base is preliminary — eight patients, no control group, no follow-up beyond the same session — and larger randomised trials have not been published. The approach is worth raising with a physiotherapist experienced in post-THA nerve-targeted techniques, particularly where abductor weakness appears disproportionate to the time elapsed since surgery.

Progression is criteria-led throughout: advance from bilateral to single-leg loading when abductor strength and single-leg stance are symmetrical, not when a fixed interval has elapsed.

When exercises are not enough — and when to seek reassessment

Intensive physiotherapy resolves most cases of Trendelenburg gait after hip replacement, but a minority of patients plateau or worsen despite months of structured rehabilitation. Before concluding that the problem is purely neuromuscular, a clinician should actively exclude structural causes — inadequate restoration of femoral offset, retained surgical hardware causing gluteal tendinopathy, or non-union of the greater trochanter. A case report published in 2024 describes a 57-year-old woman whose Trendelenburg gait persisted for two years after THA because a retained drain fragment had damaged the gluteus medius; structured physiotherapy achieved nothing until the fragment was surgically removed and the tendon augmented. These cases are uncommon, but they illustrate why persistent gait disturbance deserves imaging review rather than an indefinite extension of the same exercise programme.

Where structural causes have been excluded and conservative treatment has genuinely failed, surgical reconstruction is available. The choice depends on MRI-graded fatty infiltration of the abductor muscles, clinical severity, and how long conservative care has been pursued. Low-grade fatty infiltration may allow anatomical gluteal tendon repair. Where the gluteus medius and minimus are substantially degenerate, anterior gluteus maximus transfer — the Whiteside technique — redirects a functioning muscle to compensate for the lost abductors. High-grade soft-tissue defects with extensive fatty infiltration may require vastus lateralis transfer. These are secondary interventions, not routine, and the decision warrants consultant assessment with current imaging.

When to seek reassessment

Patients should return for assessment if:

• Trendelenburg gait persists beyond three to six months of supervised physiotherapy without meaningful improvement
• The gait pattern worsens rather than plateaus
• Lateral hip pain, snapping, or new neurological symptoms develop alongside the limp

Hip Replacement Lincolnshire, part of the MSK Doctors group, accepts patients without GP referral and offers consultant-led assessment to distinguish structural from neuromuscular causes — hipreplacementlincolnshire.co.uk.

Most lingering limps after hip arthroplasty are not permanent. The evidence reviewed across this article makes clear that Trendelenburg gait is mechanically specific: it reflects a dual failure of eccentric abductor control and concentric extensor power, sometimes compounded by nerve dysfunction or implant geometry, and it responds to rehabilitation that targets the actual impairment rather than generic leg strengthening. Identifying which factor is dominant — whether through clinical testing, gait analysis, or imaging — is what separates a rehabilitation programme that works from one that does not. That precision, more than any single exercise or technique, is the defining element of successful recovery.

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