Global assessment of hip function to avoid over- or undertreatment of hip deformities

Prasad Gourineni; Vishnu Senthil

doi:10.4103/joasis.joasis_35_22

REVIEW ARTICLE

Year : 2022 | Volume : 19 | Issue : 2 | Page : 54-56

Global assessment of hip function to avoid over- or undertreatment of hip deformities

Prasad Gourineni¹, Vishnu Senthil²
¹ Chief Orthopedic Surgeon and Managing Director, Amara Hospital, Karakambadi, Andra Pradesh, India
² Assistant Professor, Government of Orthopaedics, Government Royapettah Hospital, Chennai, India

Date of Submission	28-Oct-2022
Date of Acceptance	30-Oct-2022
Date of Web Publication	09-Feb-2023

Correspondence Address:
Vishnu Senthil
Government Royapettah Hospital, Chennai - 600 014, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/joasis.joasis_35_22

Abstract

“Four pillar concept” of hip function, consists of providing good femoral head cartilage, stable head in the acetabulum, Impingement free hip motion and optimum abductor function for any hip pathologies. In management of peadiatric and adult hip pathologies, hip optimization is achieved with the Four pillar concept.

Keywords: Abductor function, four element hip function, good cartilage, impingement, stable head

How to cite this article:
Gourineni P, Senthil V. Global assessment of hip function to avoid over- or undertreatment of hip deformities. J Orthop Assoc South Indian States 2022;19:54-6

How to cite this URL:
Gourineni P, Senthil V. Global assessment of hip function to avoid over- or undertreatment of hip deformities. J Orthop Assoc South Indian States [serial online] 2022 [cited 2023 Mar 27];19:54-6. Available from: https://www.joasis.org/text.asp?2022/19/2/54/369409

Introduction

The normal hip joint is a ball and socket joint that is optimally designed to be stable through a large range of motion. Hip function follows its form to a large extent. The shape, size, and orientation of the femoral head, neck, greater trochanter, lesser trochanter, and the acetabulum define the joint's stability, range of motion, cartilage stresses, and surrounding muscle function.^[1] The interaction between the bony structures on hip function usually cannot be assessed on imaging alone. History and physical examination are essential.

Diagnostic injections can localize the source of pain in complicated situations. A well-positioned and exposed anteroposterior view of the pelvis is essential and is adequate to assess the acetabular morphology.

Lateral view of the hip shows the anterior head–neck junction and knowledge of both the proximal and distal femur orientation is necessary to determine femoral version. 3D CT shows the femoral morphology better and magnetic resonance imaging can delineate the cartilage, ligaments, and bone marrow changes.^[2] Correlating hip morphology to its function has the potential of avoiding under- and overtreatment of hip abnormalities and planning appropriate treatment to optimize hip function. We are not aware of any previous description of such direct correlation between morphological variations and hip function.

Ideal Morphology

The ideal acetabulum covers 80% of the femoral head laterally, 20% anteriorly, and 50% posteriorly^[3],[4] [Figure 1]. The size, shape, and inclination of the sourcil match it well to the femoral head and avoid undue stress on the cartilage. The femoral head is round, well contained in the acetabulum, and congruous through a full range of motion and the fovea capitis does not contact the acetabular cartilage. The femoral neck is narrow and long enough and oriented appropriately to allow good motion in all directions and provide good abductor lever arm. We believe that radiographic symmetry of the two hips is not necessary if physical appearance, gait, and function are acceptable.

Figure 1: Red line is the anterior wall of acetabulum and blue line is the posterior wall of acetabulum. Ideal condition of noncrossover of the lines showing anteverted acetabulum

Click here to view

Variations from the ideal morphology are common even in asymptomatic hips.^[5],[6] A morphological variation may or may not cause hip problems based on how severe it is and how it interplays with the other parts of the hip.^[7] For example, coxa vara can compensate well for acetabular dysplasia and prevent lateral subluxation or add on to a deep socket to decrease motion further and cause impingement. Understanding the potential functional significance of each variation and identifying hip dysfunction are important to make an accurate clinical diagnosis.

Hip Function

The essential function of the hip is to provide pain free motion to perform routine activities as well as extreme sports. We were able to analyze hip function better by dividing it into four essential elements. This simplified the diagnosis of hip dysfunction and correlates it to hip bone morphology.

1. Good cartilage in the weight bearing dome of the acetabulum and the femoral head. Poor quality cartilage, structural defects in the cartilage, loose fragments, and inadequate surface area can cause pain and premature wear

2. Stable head in the acetabulum – Acetabular dysplasia, coxa valga, and caput valgum increase the risk of lateral instability. Increased anteversion of the femur or the acetabulum increase the risk of anterior instability

Retroversion of the femur or the acetabulum can increase the risk of posterior instability. Negative sourcil angle and coxa vara can cause medial instability and rubbing of the fovea against the acetabular fossa causing pain. Impingement on one side can make the hip unstable in the opposite direction.

3. Impingement free motion – Each hip in every person has unique motion requirements in different directions. Decreased motion from bony abnormalities cause pain from labral or extra articular tissue compression

An aspherical femoral head can crush the labrum or enter the acetabulum and cause cartilage damage. Asphericity of the head is less likely to engage the acetabulum if it is in the lower part.

Coxa breva, coxa vara, coxa profunda, and protrusio can decrease motion from the femoral neck and both trochanters being closer to the pelvis and the acetabulum.

A prominent anterior inferior iliac spine can decrease flexion of the hip.

4. Good muscle function – Abductor dysfunction causes limp and fatigue pain. It can also increase shear stresses on the acetabular cartilage.

Coxa breva and coxa valga decrease abductor lever arm, while coxa vara decreases abductor resting length. Bony prominences can cause snapping of tissues that glide over them. A laterally prominent greater trochanter can cause the ITB to snap and a prominent iliopectineal eminence can cause psoas tendon snapping.

Any variation is not clinically significant if it is not affecting hip function. The actual neck shaft angle, neck length, femoral head shape or size, acetabular index,^[8] and acetabular depth do not matter if the hip function is good.^[9]

Width of the pelvis is of cosmetic significance and can prevent wound closure with varus producing proximal femoral osteotomies in hips with long necks. Limb length discrepancy is also not considered in the “4 element” functional analysis though the pelvic tilt caused by the discrepancy can affect hip function.

Acetabular coverage will be increased on the longer side and decreased on the shorter side.^[10]

Correction of the morphology affecting any of the elements should not cause new problems with other elements. The hip capsule prevents instability in hips that are at risk and a capsulotomy in these hips needs additional measures to prevent hip subluxation or dislocation. Modern hip preservation should aim to obtain good function of all four elements of the hip with the minimal required surgery and without making future surgery more difficult or impossible.

Treatment Options and Their Consequences in Hypothetical Case Scenarios

A hip with coxa vara and breva that is impinging and has abductor weakness

Simple valgus osteotomy will help to decrease impingement by the neck, increase abductor length, and rotate the head laterally. However, the abductor lever arm shorten and the ischiofemoral space decrease further and the fovea may engage the sourcil
Relative neck lengthening (RNL) or lateralization of the greater trochanter correct abductor length and lever arm without changing the head to acetabular dome relationship and the ischiofemoral space
Morscher type of neck lengthening can increase ischiofemoral space in addition to all the improvements produced by RNL but adds an intertrochanteric osteotomy and plate fixation to the procedure

A hip with foveal impingement (fovea capitis rubbing against the acetabular dome cartilage) from caput valgum and acetabular dyspasia

Simple varus osteotomy improves hip stability and moves the fovea away from the dome but weakens the abductors, shortens the limb and increases pelvic width. Varus will also increase the risk of GT and neck impingement
RNL with varus decreases abductor weakness and impingement risk at the expense of a more complex procedure. Significant coxa vara and caput valgum is best served by RNL and further varus instead of simple varus or valgus
Periacetabular osteotomy improves hip stability and moves the sourcil lateral to the fovea and avoids any femoral surgery if a flat or slightly negative sourcil is adequate to relieve the foveal contact and maintain good function

A varus slipped epiphysis with valgus neck shaft angle or acetabular dysplasia at risk of subluxation or dislocation

Fixing the head in varus which can increase the risk of hardware failure
Full slip correction and varus peritrochanteric osteotomy
Acetabular osteotomy

Coxa valga and acetabular dysplasia will often do well with good correction of the acetabulum alone.

Summary

Variations from the ideal morphology are very common in asymptomatic hips. Each variation has the potential to cause specific hip dysfunction.

When the hip function is good, even an obvious deformity does not need correction. Correction of that variation can worsen hip function by unmasking the effect of another variation that was compensating well for the first variation. It is the responsibility of the clinician to identify the significance of each variation to avoid unnecessary correction of asymptomatic variations and correct symptomatic variations without causing new problems.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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