Hip Joint Instability After Surgery Performed Through the Surgical Dislocation Approach

Abstract

Background

Safe surgical dislocation of the hip is a versatile approach to the hip joint with a low complication rate. Hip joint instability is a devastating complication with poor prognosis.

Methods

All hips treated surgically through the safe surgical dislocation approach were entered in a database and the complication of hip joint instability was studied prospectively from 2000 to 2021. Instability was diagnosed by intraoperative stress examination and on postoperative radiographs. The initial deformities treated, type of instability, presumed causes, treatment provided, response to the treatment, and final result were recorded as they happened during the course of the treatment. We considered patient’s age, sex, body mass index (BMI), and initial diagnosis as risk factors. We evaluated the radiographs for femoral neck shortening, lack of greater trochanteric advancement, acetabular deformity, and incongruity of the hip joint. Anterior hip precautions were initiated in the middle of the study period.

Results

22/459 hips developed hip joint instability after surgical dislocation approach performed for hip preservation. Acetabular deficiency, coxa breva, coxa valga, posterior impingement, increased anteversion, lax soft tissues, medial thigh obesity and lack of postoperative precautions seemed to contribute to instability. 50% of the hips became normal. Chondrolysis and residual subluxation were common in the others.

Conclusion

Surgical dislocation approach disrupts the soft tissue restraints of the hip and joint stability depends on bony morphology, abductor muscle tension, and postoperative precautions. Several risk factors were subjective and speculative, but awareness of all the potential risk factors and prevention and treatment options should decrease this complication.

Level of Evidence

IV Case series.

Introduction

Safe surgical dislocation (SSD) is a versatile approach to the hip that allows simple and complex hip preservation procedures [1]. The approach preserves the blood supply to the femoral head consistently and has a low complication rate [2]. Major procedures like intra-articular osteotomy of the femoral neck require a wide capsulotomy and tight capsular repair was discouraged to prevent decrease in femoral head blood flow [3]. The complication of hip instability was first reported to the developer of the approach by the senior author [4]. Since then, there were three case series and two review articles on hip instability after SSD and subcapital realignment osteotomy for slipped capital femoral epiphysis [4–8]. We have noted hip instability after SSD with other procedures as well and compiled the current series to study the potential causes and treatment options.

Potential causes of hip instability in native hips, especially in the anterior direction, are acetabular dysplasia, acetabular defect from remodeling secondary to slipped epiphysis, increased acetabular anteversion, femoral head flattening, coxa breva, coxa valga, caput valgum, increased femoral anteversion, posterior impingement, capsular laxity, decreased muscle tension, increased soft tissue bulk medially, and lack of postoperative precautions [4– 11].

Materials and Methods

All hips treated with SSD approach for hip joint preservation and developed subluxation or dislocation at the end of the procedure on stress testing or spontaneously in the postoperative period were included. Patient demographics, preoperative diagnosis, primary procedure performed, type of instability, potential causes, secondary treatment provided, and outcome were recorded.

All surgical dislocation procedures were performed with the patient in the lateral decubitus position, through a straight lateral incision, trochanteric flip osteotomy, anterior capsulotomy, and dislocation as described in the original report [1]. At the end of the procedure, the hip joint was examined for range of flexion and internal rotation and for ease of anterior dislocation in extension, adduction, and external rotation. The anterior hip capsule was closed loosely, trochanteric fragment was advanced distally and fixed with two or three 3.5-mm cortical screws, and the wound was closed in layers. The hip was usually mobilized early. Weight bearing was restricted until radiographs showed evidence of osteotomy healing. Routine hip precautions against anterior dislocation by keeping the hip in flexion, abduction, and neutral rotation were started from Case # 9 onwards.

Intraoperative findings of decreased femoral head coverage, instability with stress exam, and posterior impingement were documented subjectively. Radiographic risk factors like dysplasia and femoral deformity were determined based on standard reference values [9]. The deformities were not graded for severity or compared to the values in hips that did not develop any instability. All the patients and their families were notified, and they agreed to the publication of their information.

Results

A total of 459 SSDs were performed by the senior author over 21 years for a wide range of indications including femoral head, neck, and acetabular procedures to improve the weight bearing cartilage, relieve impingement, correct hip joint instability, and improve abductor function. Of these, 22 hips were noted to have developed unexpected intra-operative or postoperative hip joint instability. The average follow-up for these 22 hips was 25 months. The hip in case #3 was converted to total hip arthroplasty (THA) early and case # 22 refused follow-up after three months. All others had at least 12 months of follow-up. The information on each patient is summarized in Table 1.

Table 1.

Demographics and details of the treatment of all hips with instability

Case	Age	Sex	BMI	Diagnosis	Procedure	Complication	Risk factors	Intervention	Outcome
1	15	M	27	Perthes disease	Cam osteoplasty	Dislocation	Acetabular dysplasia, no precautions	Closed reduction	Stiffness
2	10	M	55.2	Severe healed slipped capital femoral epiphysis	Femoral neck osteotomy	Subluxation Chondrolysis	Acetabular defect, Coxa breva, Coxa valga, Obesity, no precautions	2nd stage Varus subtrochanteric osteotomy	Chondrolysis
3	14	M	34	Avascular necrosis Head Collapse, Subluxation	Femoral neck rotational osteotomy	Collapse, Subluxation	Femoral head collapse, no precautions	Total hip arthroplasty	No symptoms
4	13	M	30	Severe stable slipped capital femoral epiphysis	Modified Dunn Osteotomy	Subluxation	No precautions	Bracing in Abduction	Normal
5	18	F	22	Mild healed slipped capital femoral epiphysis Protrusio acetabuli	Neck osteoplasty, Anterior rim trimming	Intraoperative subluxation	Protrusio acetabuli	Same stage Posterior rim trimming	Normal
6	16	M	42	Severe stable slipped capital femoral epiphysis	Modified Dunn osteotomy	Dislocation	Coxa breva, Coxa vara, Obesity, no precautions	Trochanteric advancement, bracing in abduction	Normal
7	10	F	38	Unstable slipped capital femoral epiphysis	Modified Dunn osteotomy	Dislocation	Coxa breva, Coxa vara	Trochanteric advancement	Normal
8	13	M	46	Recurrent slipped capital femoral epiphysis Avascular necrosis, Infection	Revision Dunn osteotomy	Dislocation	Coxa breva, Femoral head collapse	Closed reduction	Painful subluxation
9	14	M	39	Stable slip Chondromalacia	Modified Dunn	Subluxation	Medial thigh obesity	Open reduction, varus osteotomy	Chondrolysis
10	11	M	21	Unstable traumatic valgus slip	Modified Dunn	Intraop instability	Coxa valga, Acetabular dysplasia	Varus subtrochanteric osteotomy	Normal
11	9	F	24	Unstable slip	Modified Dunn	Intraop instability	Coxa valga, acetabular dysplasia	Varus reduction of the epiphysis	Normal
12	12	F	29	Severe stable slip	Modified Dunn	Intraop instability	Coxa valga, acetabular dysplasia	Varus intertrochanteric osteotomy	Normal
13	15	M	24	Unstable slip, screw fixation, AVN	Modified Dunn, Ibandronate injection	Subluxation	Partial collapse	Abduction bracing	Chondrolysis
14	13	M	37	Avascular necrosis, collapse	Head reduction osteotomy	Subluxation	Medial obesity, no precautions	Abduction bracing	Subluxation
15	14	M	39	Unstable slip Avasular necrosis	Head reduction osteotomy	Subluxation	Coxa breva, medial obesity	External fixator application	Subluxation
16	14	F	36	Healed slip	Neck osteotomy	Subluxation	No precautions	None	Chondrolysis
17	11	F	22	R caput valgum, acetabular dysplasia	RNL, varus	Subluxation	Mild head collapse	None	Normal
18	16	F	24	L caput valgum acetabular dysplasia	RNL, varus	Subluxation	Genu valgum	Contralateral shoe raise, distal femur osteotomy	Normal
19	10	F	19	Dislocation, dysplasia, coxa breva	RNL, Varus, Colonna, Shelf	Subluxation	Head collapse	None	Subluxation
20	21	F	23	Dislocation Dysplasia	Colonna, Shelf	Subluxation	Inadequate precautions	Abduction Spica	Normal
21	13	M	22	R hip dysplasia, caput valgum	RNL, Varus, Dega	Subluxation	Acetabular dysplasia	Abduction spica	Dysplasia
22	19	M	26	L hip dysplasia, subluxation, coxa valga, spasticity	Varus, RNL, PAO	Subluxation	Recurrent acetabular dysplasia	None	Subluxation

There were 13 male and nine female patients with an average age of 13.7 years and average BMI of 29.2. Primary diagnosis of the hip was SCFE in 13, hip dysplasia with major femoral deformity in six, avascular necrosis in two, and Perthes deformity in one hip. The primary procedure was femoral neck osteotomy in 12, femoral neck lengthening and varus osteotomy in 6, femoral neck osteoplasty in 2, femoral head reduction osteotomy in 2. Additional procedures planned and performed in the same stage were Colonna capsular interposition osteoplasty in two, peracetabular osteotomy in one, and Dega osteotomy in one hip. Procedures performed under the same anesthetic to correct instability noted intraoperatively were posterior acetabular rim trimming in one and varus producing femoral procedures in three hips. Fig 1A & 1B are radiographs of patient 2 and Fig 2A & 2B are radiographs of patient # 6. 

Fig. 1.

Case 2. 10 year old obese male with bilateral severe slipped epiphysis. A Lateral subluxation of the left femoral head into the acetabular defect due to excessive neck shortening and inadequate trochanteric advancement after left femoral neck osteotomy for severe healed slip. B AP pelvis with chondrolysis of the left hip in spite of correction of instability with varus subtrochanteric osteotomy. The right hip did well after healing of the modified Dunn osteotomy

Fig. 2.

Case 6. 16 year old male with severe right hip slip. A Right hip dislocation one week after modified Dunn Osteotomy. White arrow pointing to the medial thigh obesity. B Right hip stabilized after greater trochanter advancement and postoperative precautions

Eighteen hips developed postoperative instability, subluxation in 14 and dislocation in 4 hips. Second stage interventions to correct instability were abduction brace/cast in seven, open reduction and greater trochanter advancement in two, varus osteotomy in two, external fixator application in one, and total hip arthroplasty in one hip. Four hips did not receive further treatment.  All risk factors and final outcomes are listed in Table 2.

Table 2.

Risk factors for hip instability and final outcomes of all patients

Pre-existent factors	Surgical factors	Postoperative factors	Final outcome
Acetabular dysplasia—9	Coxa breva—5	Femoral head collapse—3	Normal—11
Medial thigh obesity—5	Abductor laxity—2	Recurrent dysplasia—2	Subluxation—5
Coxa valga—3	Caput valgum—1		Chondrolysis—4
Protrusio—1			Acetabular dysplasia—1
Genu valgum—1			Stiffness—1

Discussion

Surgical dislocation is a useful approach allowing a wide spectrum of hip joint preservation surgeries. The reported complication rate using this approach is low; especially, the rate of avascular necrosis [2]. Hip instability after this surgery has not been reported and no specific precautions were recommended initially. Our experience with this procedure was predominantly for severe deformities and we noted hip joint instability also with procedures other than femoral neck osteotomies for slipped epiphysis. We had 13 hips with SCFE as the primary diagnosis while nine others had other diagnoses.

The hip instability after surgical dislocation in our cases was probably due to a combination of extensive capsulotomy and predisposing factors though we had two hips without any risk factors suggesting that the approach itself can render a hip unstable. Hence, we recommend routine hip precautions against anterior subluxation in all hips till the soft tissues adjust to the new hip morphology. We chose four weeks for the restrictions because we did not notice any new instability episodes beyond this period.

Among preoperative factors, we found hip morphological factors like acetabular dysplasia in nine, coxa valga in three, and posterior impingement from protrusio in one hip. Ipsilateral genu valgum induced hip adduction in stance could have contributed to hip instability in one patient. Medial thigh obesity can apply lateral subluxatory forces when the legs are brought together acting like a large perineal post that induces a lateral vector during hip distraction. This was suspected to be a contributor in five hips. No age, sex, or BMI cutoff were identified.

Among factors produced by the primary surgical procedure, excessive femoral neck shortening (coxa breva) in five hips, laxity of hip abductor muscles from inadequate trochanteric advancement in two hips, and valgus alignment of the head in one hip were suspected. All remedial procedures were femoral sided except for posterior acetabular rim trimming in one hip because the femur was already well exposed and acetabular surgery might have required additional dissection or a change in patient position. Femoral sided procedures to compensate for acetabular deformity cause femoral deformity and limb shortening.

Among postoperative factors, recurrent dysplasia in two hips and collapse of the femoral head in three hips were suspected as the causes. Both these causes are well known to cause hip instability even when surgical dislocation approach was not used. Adequate precautions could have prevented instability in at least the six hips that stabilized with nonoperative abduction alone.

Final outcome was normal in 11 hips (50%) of our cases. AVN was the most common complication in series by Upasani [8]. We did not find AVN as a complication but it was a cause in three hips. We noted chondrolysis or rapid joint narrowing in four hips. All four hips were preserved with some improvement of the joint space over time. Five hips had subluxation at final follow-up, two of them were untreated. Only one hip could not be preserved and was converted to THA early.

Limitations of our study are 1. It is a retrospective case series with no comparative analysis. 2. Our determination of the various risk factors in each hip was speculative, but previous experience, common knowledge and the response to treatment support these presumed causes.

In conclusion, we propose the following checklist.

1. Preoperative risk factors such as acetabular dysplasia, coxa valga, caput valgum, increased femoral and acetabular anteversion, coxa profunda, genu valgum, and medial thigh obesity require correction or compensation to prevent postoperative dislocation.

2. All hips should undergo intra-operative dynamic testing of the hip in adduction, extension, and external rotation before closure to identify and correct anterior instability. Hip motion and stability are products of overall hip morphology and decreased motion in one direction causes impingement that induces instability in the opposite direction.

3. Posterior impingement, decreased head coverage, neck shortening, valgus reduction, lack of abductor tensioning should be avoided or identified and corrected.

4. Strict postoperative precautions are required in high-risk patients by maintaining the hip in flexion, abduction, and internal rotation for a few weeks. Careful mobilization is required during this period to prevent stiffness.

Declarations

Conflict of Interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.