Why these three milestones define mid-phase recovery

Around week six after hip replacement, the focus shifts. Wound healing is largely complete, basic weight-bearing is established, and the question changes from 'am I safe to move?' to 'how far along am I, really?' The answer, in clinical practice, comes down to three things a physiotherapist can observe and measure: stair climbing, hip range of motion, and single-leg stance on the operated side.

These three milestones are not arbitrary. Each one probes a different layer of recovery. Stair climbing tests load tolerance — whether the hip and its surrounding muscles can accept full body weight through a dynamic, cyclic movement. Hip range of motion, particularly flexion beyond 90°, reflects how far the joint has recovered its mechanical freedom. Single-leg stance on the operated limb tests something more subtle: the neuromuscular system's ability to hold the pelvis level without compensating through the trunk or the opposite leg.

The three are also tightly linked in practice. Achieving flexion beyond 90° is a prerequisite for the reciprocal step-through pattern on stairs; abductor control determines whether a patient can descend stairs safely without the pelvis dropping; pelvic stability in turn feeds both. Outcome tools such as the Harris Hip Score and Berg Balance Scale give clinicians consistent reference points for tracking these interdependencies across time and between patients.

How quickly mid-phase milestones can be safely pursued depends in part on the surgical approach used — a distinction this article returns to throughout.

Hip ROM targets and what the 90° precaution actually means

The accepted ROM targets for weeks six to twelve after hip replacement are 110–120° of flexion, 20° of extension, and 30–40° of abduction. Reaching these figures matters because each one unlocks a functional capability: 110° of flexion is the threshold at which reciprocal stair climbing and comfortable seated posture become mechanically possible; extension and abduction feed the hip's ability to propel and stabilise during walking.

For patients who have had a traditional posterior hip replacement, the path to those flexion targets is governed by the 90° precaution — a strict instruction to keep the hip below 90° of flexion for approximately 90 days post-operatively. The restriction exists for a specific anatomical reason: the posterior approach severs the short external rotator tendons (a group of small muscles at the back of the hip that normally hold the femoral head in the socket). While severed, those structures cannot adequately resist dislocation if the hip is flexed beyond 90°. The 90-day window reflects the time the tissues require to heal and reattach securely enough to perform that function again.

SPAIRE — Saves Piriformis And Obturator Internus with Repair of Obturator Externus — uses the same posterior access route but leaves those tendons intact. Because the structures are not divided, the biological restriction that generates the 90° rule does not apply in the same way, and ROM progression can theoretically begin earlier. Proprioceptive feedback from the preserved tendons also remains intact, which has implications for balance control discussed in the following section.

It is worth being precise about what this difference does and does not mean. Earlier ROM progression is made available, not guaranteed; individual pain levels, swelling, and abductor strength still determine the actual pace. Progression should be criteria-based — advancing when movement is pain-free and pelvic control is adequate — rather than driven by calendar weeks alone.

Single-leg stance and the Trendelenburg sign

Standing on the operated leg — without the pelvis dropping toward the other side — is the defining balance milestone of mid-phase hip replacement rehabilitation. In clinical terms, the target runs from holding 10–20 seconds with fingertip support on a surface, progressing to 30–60 seconds fully unsupported, and eventually to the same task on an uneven surface where the hip cannot rely on a stable floor to compensate.

When the pelvis does drop toward the non-operated side during this test, it signals a positive Trendelenburg sign. In plain terms, this means the muscles on the operated hip's outer side — principally gluteus medius — are not generating enough force to hold the pelvis level against gravity. The operated leg is on the ground and the muscles around it should be doing the work; pelvic drop confirms they are not yet strong or co-ordinated enough to do so.

This is not a rare or transient finding. A 2024 gait analysis study of 89 THA patients found that 27% still showed Trendelenburg gait at a mean of 1.3 years post-operatively. Multiple regression identified reduced eccentric hip abductor contraction and reduced concentric hip extensor contraction as the significant determinants — meaning this gap is driven by specific, addressable muscle deficits rather than by time passing alone.

Clinicians treat the single-leg stance milestone with corresponding seriousness beyond the arthroplasty context. A 2022 study published in the British Journal of Sports Medicine, involving 1,702 adults aged 51–75, found that inability to hold a 10-second one-legged stance was independently associated with 84% higher all-cause mortality (HR 1.84, 95% CI 1.23–2.78) after adjusting for age, sex, BMI, and comorbidities. That figure is not intended to alarm — it reflects the broader health status that poor balance tends to represent — but it is why physiotherapists treat this milestone as more than a balance exercise.

The primary tools for building abductor control are straightforward: side-lying hip abduction, clamshell exercises, and lateral resistance-band walks. These remain central to mid-phase rehabilitation regardless of which surgical approach was used, though the proprioceptive continuity available in tendon-sparing procedures such as SPAIRE may support earlier neuromuscular re-education.

Stair climbing: the integrative test of hip replacement recovery

Climbing a flight of stairs looks straightforward — and that is precisely why it works so well as a rehabilitation marker. The task cannot be broken down into components in the way that isolated exercises can. To negotiate even a single step safely, the operated hip must produce enough flexion to clear the riser, sustain single-leg load while the other foot lifts, and generate hip extensor and abductor force to drive the body upward. ROM, strength, and confidence are demanded simultaneously. That combination is why stair performance appears as a primary discharge milestone after total hip arthroplasty and continues to feature in outcome tracking years post-operatively.

The clinical rule that governs technique is universally taught: up with the good, down with the bad. Leading upstairs with the non-operated leg reduces the peak flexion demand on the replaced hip at the moment of greatest load; leading downstairs with the operated leg controls the eccentric loading during descent. A handrail is used throughout the early stages, with a walking aid carried in the opposite hand if balance requires it.

Progression runs in four practical phases. In weeks one and two, the task is a step-to pattern — both feet meet on each step — with handrail and walking aid. Weeks two to six introduce the full stair flight as walking aids are progressively reduced and hip muscle strength accumulates. The critical threshold arrives between weeks six and twelve: the reciprocal, step-through pattern where each foot moves to a separate step. This is not simply a safety upgrade; it confirms that the operated hip can tolerate full cyclic single-leg load, which is the functional marker of genuine mid-phase recovery. Beyond three months, unrestricted stair use — including without a handrail where confidence and strength allow — becomes the realistic target.

One question patients often raise is whether their implant type affects how quickly they reach these stages. A 2025 propensity-matched study of 232 THAs found that cemented stems produced earlier T-cane walking than cementless stems, but stair-climbing time showed no significant difference between the two fixation methods. The finding is practically reassuring: stair progress is determined principally by muscle recovery, not by whether the stem was cemented in. That places the rate-limiting factor squarely within the rehabilitation programme rather than in the operating theatre.

How surgical approach shapes milestone timing

The decision taken in the operating theatre shapes rehabilitation months before physiotherapy begins. Which soft tissues are cut, preserved, or repaired determines the biological constraints a patient works within during mid-phase recovery — and those constraints, more than any fixed calendar, set the pace at which each milestone can safely be pursued.

Standard posterior THA severs the short external rotators — piriformis, obturator internus, and obturator externus — to gain access to the joint. As the preceding section on ROM established, reattachment of these tissues requires approximately 90 days, sustaining the 90° flexion precaution throughout. In practical terms, this means the step-through stair pattern and comfortable seated function both depend on ROM that is actively prohibited during the same weeks in which patients are also building abductor strength. The two constraints compound each other.

SPAIRE (Saves Piriformis And Obturator Internus with Repair of Obturator Externus) uses a posterior access route but keeps those tendons intact throughout the procedure. Because no severed structures require a healing window, the 90° precaution is removed, theoretically permitting earlier progression towards functional ROM and, with it, earlier attempts at reciprocal stair gait. Preserved mechanoreceptors within the intact tendons may also support proprioceptive continuity, potentially assisting abductor re-education during single-leg stance work.

Anterior approaches avoid posterior soft-tissue disruption altogether but involve different muscle-interval considerations, and hip extension precautions may apply instead — so the constraint shifts rather than disappears.

Across all approaches, a meaningful evidence gap remains: no large randomised controlled trials have directly compared milestone timing by surgical route. Available guidance rests on mechanistic reasoning and smaller observational series rather than head-to-head trial data. This reinforces the case for criteria-based progression — advancing when objective markers such as controlled single-leg stance, adequate ROM, and stair-load tolerance are genuinely met — rather than following any approach-derived fixed timeline, because individual variation is substantial regardless of how the hip was accessed.

What these milestones mean beyond mid-phase

Clearing the three milestones — adequate ROM, controlled single-leg stance, and reciprocal stair gait — sets a functional floor, not a finishing line. A patient who reaches these thresholds by week twelve has demonstrated that the replaced hip can sustain the demands of daily life, but the evidence indicates the recovery trajectory continues well beyond them.

The Trendelenburg prevalence figure introduced earlier — 27% of patients at a mean of 1.3 years post-operatively, despite broadly acceptable self-reported scores — is the clearest illustration of this gap. In that cohort, subjective satisfaction and objective muscle performance had diverged: eccentric abductor and concentric extensor force production remained measurably deficient on gait testing even when patients reported functioning well. That discrepancy does not always resolve without targeted intervention.

Movement compensations established during months of pre-operative pain compound the picture. Neuromuscular patterns that protected a deteriorating joint do not automatically reset once the joint is replaced, and deliberate re-education often extends into the late post-operative phase.

Structured strengthening of the hip abductors, glutei, and extensors continues to yield meaningful gains from three to twelve months post-operatively, improving walking endurance, load tolerance, and stair confidence well after mid-phase discharge criteria are met. A patient whose hip feels "not quite right" despite acceptable clinical scores may have residual abductor or extensor deficits that routine clinical observation alone does not reliably detect. Objective gait analysis, where available, can quantify these gaps with enough precision to direct late-phase rehabilitation — and distinguish a plateau from a recovery that still has meaningful distance to run.

1. [1] Successful 10-second one-legged stance performance predicts survival in middle-aged and older individuals. (2022). https://doi.org/10.1136/bjsports-2021-105360 https://doi.org/10.1136/bjsports-2021-105360
2. [2] Trendelenburg gait after total hip arthroplasty due to reduced muscle contraction of the hip abductors and extensors. (2024). https://doi.org/10.1016/j.jor.2024.07.020 https://doi.org/10.1016/j.jor.2024.07.020
3. [3] Advantages of cemented stems in facilitating early postoperative rehabilitation after total hip arthroplasty. (2025). https://doi.org/10.1177/11207000251388580 https://doi.org/10.1177/11207000251388580