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Titel på arbejdetThe efficacy of surgical approach on patient‐reported outcomes, gait and hip muscle strength in patients with hip osteoarthritis after total hip arthroplasty. A comparison of the posterior approach with the lateral approach – COMPALA
NavnSigne Rosenlund
Afdeling / StedDepartment of Orthopaedic Surgery and Traumatology, Odense University Hospital and Køge Hospital
UniversitetUniversity of Southern Denmark
  • Hip and knee surgery
Abstract / Summary

Background: Hip osteoarthritis (OA) is a major cause of disability worldwide. Total hip arthroplasty (THA)
is a successful symptomatic treatment of hip OA and has been declared as ‘the operation of
the century’. Despite its great success on important key‐endpoints, not all patients are
satisfied. Results based on patient‐reported outcomes (PROs) have shown that some patients
after THA experience a reduction in physical function, limping gait and a reduced quality of
life compared to the healthy population. The choice of surgical approach is one factor that
may affect the PROs, gait pattern and hip muscle strength. Worldwide, the use of the posterior
approach (PA) and the lateral approach (LA) are dominating. One major difference between
the two approaches is the surgical detachment of the hip abductor muscles (gluteus medius
and minimus) which is only performed during the LA procedure. This surgically induced
damage of the hip abductors may cause reduced hip muscle strength, changes in gait function
and reduced PROs, especially those associated with physical function. The literature reveals
that the optimal choice of surgical approach based on evidence from high level studies
remains unclear.

Thus, the overall aim of this thesis was to investigate in a randomised controlled trial if
patients with primary hip OA operated on with the PA improved more in PROs, hip muscle
strength and gait function than patients operated on with LA 12 months post‐operatively. The
secondary aim was to explore the use of a composite gait index – the Gait Deviation Index
(GDI) in the quantification of hip OA patients’ gait pathology. The GDI is thought to be a
general measure of the overall gait ‘quality’. A high GDI score was hypothesised to be
associated with better hip muscle strength and PROs.

Method: In total, 80 patients aged 45 to 70 years with unilateral primary hip OA were
scheduled for primary cementless THA and randomised to surgery with either PA or modified
direct LA. The patient‐reported questionnaire Hip Disability and Osteoarthritis Outcome
Score (HOOS)‐Physical Function subscale was used as the primary outcome. Secondary
outcomes were the HOOS‐Pain, HOOS‐Quality of Life, the EQ‐5D‐3L, UCLA activity score and a
limping score. The patients completed the questionnaires pre‐operatively and at 3, 6 and 12
months post‐operatively. The data were analysed with the multilevel mixed linear model
analysis (with repeated measures) evaluating the mean difference in improvement between
the PA and LA groups with the primary end‐point being 12 months.
A subgroup of 47 patients was randomly allocated to 3‐dimensional gait analysis and
assessment of isometric maximal voluntary hip muscle strength (iMVC) in abduction, flexion
and extension and finally pain during these tests was measured using the ‘Numeric Rating
Scale for Pain’ (NRS). Associations between the GDI, hip muscle strength, NRS‐pain and HOOSsubscale
scores were analysed. The same 47 patients were also evaluated at 3 and 12 months
post‐operatively with the same protocol as that used pre‐operatively.

Results: Seventy‐seven patients were available for intention‐to‐treat analyses. The results
showed no difference in improvement in HOOS‐Physical Function between the treatment
groups at 12‐months: ‐3.3 [95% CI: ‐8.7 to 2.1]. All secondary outcomes showed similar
results except for limping score, where PA patients improved more than LA patients: 0.4 [95%
CI: 0.05 to 0.66] points on a 4‐point Likert scale.
The results from the subgroup of 47 patients showed that the GDI was positively associated
with hip abduction strength, hip flexion strength, HOOS‐Physical Function, HOOS‐QOL, and
negatively associated with pain after walking. All the associations were weak to moderate and
explained 13% to 25% of the variation in the GDI.
The results from the follow‐up study showed no difference in between‐group improvement
nor within‐group improvement in the GDI. However, we found a statistically significantly
difference in improvement in both hip abductor and flexor muscle strength in favour of the PA
group: ‐0.20 (Nm/kg) [95% CI: ‐0.4 to 0.0] and ‐0.20 (Nm/kg) [95% CI: ‐0.4 to 0.0]

Conclusion: Better gait ‘quality’ measured with the GDI was associated with better hip muscle
strength, pain and PROs pre‐operatively. Patient‐reported physical function, pain and quality
of life in patients treated with PA did not improve more than patients treated with LA at 12
months post‐operatively. However, patients in the PA group improved more in self‐reported
limping than the LA patients. This positive effect on limping gait in the PA group might be
explained by a greater improvement in hip abductor and flexor muscle strength in the PA
group. However, we found no difference in gait function between groups.

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