Complications of hip preserving surgery.

Preoperative evaluation of the pathomorphology is crucial for surgical planning, including radiographs as the basic modality and magnetic resonance imaging (MRI) and case-based additional imaging (e.g. 3D-CT, abduction views).Hip arthroscopy (HAS) has undergone tremendous technical advances, an immense increase in use and the indications are getting wider. The most common indications for revision arthroscopy are labral tears and residual femoroacetabular impingement (FAI).Treatment of borderline developmental dysplastic hip is currently a subject of controversy. It is paramount to understand the underlining problem of the individual hip and distinguish instability (dysplasia) from FAI, as the appropriate treatment for unstable hips is periacetabular osteotomy (PAO) and for FAI arthroscopic impingement surgery.PAO with a concomitant cam resection is associated with a higher survival rate compared to PAO alone for the treatment of hip dysplasia. Further, the challenge for the surgeon is the balance between over- and undercorrection.Femoral torsion abnormalities should be evaluated and evaluation of femoral rotational osteotomy for these patients should be incorporated to the treatment plan. Cite this article: EFORT Open Rev 2021;6:472-486. DOI: 10.1302/2058-5241.6.210019.

Over the past two decades, substantial increase in the knowledge of pre-arthritic conditions of the hip joint including femoroacetabular impingement, development dysplasia of the hip, slipped capital femoral epiphysis, residual deformities after Perthes disease, torsional abnormalities together with the development of new surgical approaches and procedures, have revolutionized the field of joint preserving surgery. The utilization of joint preservation operations including hip arthroscopy, surgical hip dislocation, and periacetabular osteotomy (PAO) has increased over time.[1]

The purpose of this article is to review current knowledge about complications of joint preservation procedures of the hip.

Preoperative workup

A workup of the patient’s symptoms, clinical findings and standardized radiographic workup is mandatory in patients eligible for joint preserving surgery. Detailed understanding of the location and extension of the deformity is essential for the correct choice of surgical technique and success of the surgical treatment. Patients may present typical symptoms (e.g. groin pain with hip rotation, while sitting or during sport activities; trochanteric pain). A detailed clinical examination of the hip may further present typical findings (e.g. restricted range of motion, positive anterior impingement sign).[2-4] Conventional radiographs remain the basis of the radiographic workup. These should include supine anteroposterior (AP) pelvic views to asses radiographic joint degeneration, acetabular coverage, acetabular version and gross anatomy of the pelvis.[5] To detect accompanying cam deformities, which are typically located anterosuperiorly, an axial view is needed. In the absence of severe joint space narrowing, magnetic resonance imaging (MRI) of the hip should be performed in all patients evaluated for joint preserving surgery. At first, fluid-sensitive images with a large field of view should be obtained to screen for associated inflammatory or neoplastic conditions surrounding the hip joint.[6] Fast axial images of the pelvis and the distal femoral condyles should be acquired to assess femoral torsion.[7] Then dedicated high-resolution images of the hip at field strengths of 1.5 T or 3 T in the coronal, axial-oblique/axial and sagittal orientations should be performed to assess intraarticular lesions.[8] Acquisition of radial images is essential to provide a circumferential assessment of the femoral head neck junction.[9,10] Although promising results have been demonstrated for non-contrast MRI of the hip at 3 T, direct MR arthrography is still the current diagnostic gold standard in the detection of chondrolabral lesions.[11-13] MR arthrograms provide crucial prognostic information as extensive cartilage defects, acetabular cysts and osteophyte formations indicate a higher risk for failure of femoroacetabular impingement (FAI) surgery in the long term.[14] Injection of intraarticular contrast agent further enables application of leg traction to achieve joint distraction and has shown promising early results to improve the visualization of intraarticular lesions.[15-18]

Further on, selective additional imaging may be added. To asses for joint congruency, functional views are performed. Especially in dysplastic hips there is typically an apparent joint space narrowing due to subluxation and for differentiation the abduction view is used.[19] New biochemical cartilage MRI techniques such as delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) or T2* imaging offer the ability to evaluate chondral defects more accurately before surgical therapy.[20,21] Three-dimensional computerized tomography (3D CT) scans enable exact visualization of the bony deformities, and specific software for dynamic range of motion simulation can be very effective to identify the dominant osseous deformity and plan surgical correction.[22] This is especially true for surgical planning in cases with suspected extraarticular FAI.[23] 3D MRI has great potential to replace 3D CT for rendering of 3D models of the hip joint and further analysis for a non-invasive improved surgical decision-making in these mostly young patients.[24-26]

Hip arthroscopy (HAS)

Historically the treatment of hip pathologies including FAI and labral tears has required open surgical hip dislocation.[27] Over the past years HAS has undergone tremendous technical advances, an immense increase in use and the indications are getting wider.[28-30] Thus, a wide range of complications is more frequently seen and reported (Table 1; Fig. 1). Generally complications are rare (1.3–4.2%),[28,31-33] but may be underreported.[33,34]

Table 1.

Complications of hip arthroscopy (HAS) are listed below with grading according to Sink et al.[118]

Grade	Complication	Prevalence	Reference
1 Complication without clinical relevance	Superficial wound infection	< 1%	[119]
	Heterotopic ossification Grade 1–2 (Brooker)	< 1–6%	[119–122]
	Instrument breakage	< 1%	[119,122,123]
	Iatrogenic chondral injury	3%	[119,124]
	Iatrogenic labral injury	< 1–20%	[119,125]
	Hypothermia	2.7%	[126]
2 Complication with outpatient or medication treatment	Temporary nerve injury	2–7%	[119,122,123,127]
	Permanent nerve injury	< 1%	[122]
	Perineal skin damage	< 1%	[119,122,123,128]
	Deep wound infection	< 1%	[119,129]
3 Complication with surgical therapy or unplanned hospitalization	Deep vein thrombosis	< 1–3.7%	[119,130]
	Femoral neck fracture	< 1%	[119,123]
	Scrotal skin necrosis	< 1%	[131]
	Avascular necrosis	< 1%	[119,123]
	Heterotopic ossifications Grade 3–4 (Brooker)	< 1%	[120]
	Extraarticular fluid extravasation	< 1–1%	[119,122,123]

Fig. 1

A 34-year-old patient presented with postoperative hip pain following arthroscopic rim trimming and labrum refixation in an external institution. (A) Anteroposterior pelvis view shows a preserved joint space and no obvious deformity. (B) Computerized tomography of the hip showed a drill hole and suspected intraarticular position of the anchor. (C) Patient underwent subsequent surgical hip dislocation which confirmed the intraarticular anchor position and resulting co-located acetabular cartilage damage.

The early arthroscopic treatment method of labral tears was debridement.[35] Based on increasing understanding and research on labral function and its relation to joint stability, management has progressed to favour repair when sufficient tissue is available or even reconstruction in cases in which the labrum was not amenable to repair.[36-40] Reestablishment of suction seal and normal biomechanics of the hip joint is allowed by labral repair.[41] This has further been substantiate in several case-control studies comparing patient-reported outcomes (PROs) of labral repair to debridement reporting significantly better outcomes for patients undergoing repair.[42-44] Further on, reconstruction has become a more widely used treatment option in cases where the labrum is not amenable to repair.[27] Several studies have demonstrated that reconstruction can closely approximate the native labrum and lead to favourable outcomes in the short term despite variable techniques, graft type and indications.[39,40]

The most common indications for revision arthroscopy are labral tears and residual FAI.[45] In a systematic review labral tears were commonly treated with labral reconstruction at the time of revision.[45] The corresponding improvement in outcomes may suggest that labral degeneration is one of the leading sources of pain in the failed hip arthroscopy.[45] In systematic reviews of revision hip arthroscopy, residual cam or pincer lesions not properly addressed in the index procedure were found to be the most common indication for revision arthroscopic surgery and the most common intraoperative finding.[46,47] Under-resection of cam lesions may leave residual impingement[48] and consequently further chondrolabral damage that may result in cartilage degeneration.[49] Residual cam deformities were addressed in up to 37% of the patients undergoing revision HAS.[47] On the other hand over-resection may cause fractures of the femoral neck, disruption of the labral seal, or mechanical symptoms.[50,51] Femoral neck fractures may occur due to weakening of the bone and thus most postoperative protocols limit weight bearing (Fig. 2).[50] A cadaveric study found that the load-bearing ability of the bone was not affected if resection of up to 30% of the anterolateral head–neck junction was performed. The sealing effect is dependent on the fit of the labrum against the femoral head and thus over-resection may disrupted this seal of the labrum against the over-resected area.[50,52] This leads to impaired joint lubrification and quicker cartilage consolidation.[52]

Fig. 2

(A) Preoperative anteroposterior pelvis view of a 27-year old professional football player with cam femoroacetabular impingement who underwent arthroscopic cam resection. (B) Ten months following return to play, the patient presents with recurrent hip pain. The corresponding radiograph shows no obvious pathology. (C) The coronal fluid sensitive magnetic resonance image of the hip shows bright bone marrow oedema with sclerotic line corresponding to a stress fracture. (D) Stabilization of the stress fracture was performed using cannulated screws.

For arthroscopic treatment of FAI less favourable outcomes have been reported for patients of older age groups (> 45 years), female sex, those with elevated body mass index (BMI), osteoarthritic changes, decreased joint space (< 2 mm), chondral defects, increased lateral centre edge (LCE) angle and labral debridement compared with labral repair.[53]

The ideal treatment of borderline developmental dysplastic hip (BDDH) is currently a subject of controversy. It is paramount to understand the underlining problem of the individual hip and distinguish instability (dysplasia) from FAI as the appropriate treatment for unstable hips is PAO and for FAI arthroscopic impingement surgery. The consequences of hip arthroscopy in unstable hips can be devastating (Fig. 3).[54-57] Mostly, BDDH is defined as LCEA of 18–25°[58] and to further evaluate stability the Femoro-Epiphyseal Acetabular Roof (FEAR) Index was introduced,[59] which helps to separate the indications of PAO or hip arthroscopy. Among patients with an LCEA of ≤ 25°, a FEAR Index of < 5° is a moderate indication for hip arthroscopy.[59] Instability due to deficient coverage further leads to increased loads to the labrum, resulting in labral hypertrophy[60-62] and an increased iliocapsularis-to-rectus-femoris ratio is suggestive for instability in BDDH.[63] Surgically, capsular closure or capsular plication is paramount. Failure to completely close the capsulotomy site may lead to iatrogenic instability and patients may be more likely to have residual symptoms from capsular laxity or capsular defects (Fig. 4).[64]

Fig. 3

(A) A 26-year-old female patient with borderline developmental dysplastic hip and persistent hip pain following two external hip arthroscopies with offset correction and labrum debridement. Anteroposterior (AP) pelvis view shows insufficient acetabular coverage with an lateral centre edge angle (LCE) of 18°. (B) Magnetic resonance arthrography was performed for evaluation of intraarticular lesions. Radial images show hypoplastic labrum with intrasubstance tearing (arrow). Contrast interposition (arrowheads) at the posterior inferior acetabulum, corresponding anterior translation of the femoral head indicative for hip instability. (C) AP pelvis view six months after periacetabular osteotomy shows improved lateral acetabular coverage with an LCE of 27°.

Fig. 4

(A, B) A 33-year-old patient with normal acetabular coverage and mild cam deformity and partial labrum tear (arrow) anterosuperiorly who underwent arthroscopic cam resection and labrum refixation. (C) Patient presented with prolonged pain postoperatively and repeated magnetic resonance arthrography showed extensive defect of the anterior capsule (arrowheads). The patient was scheduled to capsule reconstruction subsequently.

Surgical hip dislocation (SHD)

Open surgical hip dislocation (SHD) offers the possibility of circumferential corrections and can be combined with additional procedures to relieve intra- and extraarticular impingement and associated collateral damages. The technique was first described by Ganz et al[4] in 2001 as a technique for safe surgical dislocation of the hip after detailed analysis of the blood supply of the femoral head.[65] The approach can be used for surgical correction of pre-arthritic conditions such as FAI,[2] residual Perthes deformity (Legg-Calvé-Perthes disease),[66] slipped capital femoral epiphysis (SCFE),[67] avascular necrosis of the femoral head (AVN), synovial disease with formation of loose bodies and for open reduction and internal fixation (ORIF) of acetabular fractures.[68]

The rate of severe complications after SHD for FAI is generally low (Table 2). Persisting groin pain can be present in approximately 10% to 15% of patients after open FAI surgery.[69] Insufficient correction of the femoral and acetabular deformity, advanced osteoarthritis and intraarticular adhesions[70] are causes of persistent groin pain after FAI surgery.[71] Patients often report no or only a short pain-free interval after surgery when a persistent FAI morphology is present. Residual deformity is the most common cause of persistent hip pain and persistent FAI after previous FAI surgery.[72] Adhesions may be present in up to 62% of patients undergoing revision surgery.[73] Typical locations for adhesions are between the joint capsule and the former resection area of the femoral neck (Fig. 5), and between the labrum and the joint capsule.[69] Diagnostics are performed with MR arthrography,[74] and treatment of painful adhesions is generally by HAS.[69] Inadequate postoperative mobilization and patients aged under 30 years are at increased risk.[75]

Table 2.

Complications of surgical hip dislocation (SHD) are listed below with grading according to Sink et al.[118]

Grade	Complication/Consecutive Surgery	Prevalence	Reference
1 Complication without clinical relevance	Superficial wound infection	0.6–1 %	[132,133]
	Bursitis trochanterica	12.5%	[134]
	Heterotopic ossifications Grade 1–2 (Brooker)	5.4%	[132]
2 Complication with outpatient or medication treatment	Partial neurapraxia	0.3–1.5%	[4,132]
3 Complication with surgical therapy or unplanned hospitalization	Heterotopic ossification Grade 4 (Brooker)	1.4%	[134]
	Trochanteric fixation failure	1–1.8%	[132–135,135]
	Evacuation of wound haematoma	2%	[133]
	Removal of trochanteric screws	25–64.4%	[133,135]
	Arthroscopic adhesiolysis	6%	[133]
	Revision of iliotibial band dehiscence	1%	[133]

Fig. 5

A 24-year-old patient with persistent pain after surgical hip dislocation for mixed femoroacetabular impingement. Magnetic resonance arthrography presents adhesions between the joint capsule and the femoral neck (arrowheads). The patient underwent hip arthroscopy for adhesiolysis.

Eighty per cent of patients undergoing SHD for correction of anterior intraarticular FAI have a good clinical result without osteoarthritis progression and no total hip arthroplasty at 10-year follow-up.[76] One could count failure of the procedure and disease progression as complications, and several predictive factors for an unfavourable outcome after SDH have been reported (Table 3). In a retrospective study, a 10-year survivorship of 82% was reported after SHD for acetabular fractures involving the posterior wall or transverse and posterior wall or others.[77] Predictors for failure were femoral chondral lesions, marginal impaction, duration of surgery, and age of patient.[77]

Table 3.

Predicted factors for failure of surgical hip dislocation (SHD) for femoroacetabular impingement (FAI) at 10-year follow-up according to Steppacher et al.[76]

Category	Predictive factors
Demographic factors	Age > 40 yearsBMI > 30 kg/m2
Preoperative radiographic factors	Anterior femoral coverage < 15%Osteoarthritis ≥ Tönnis Grade 1
Postoperative factors related to surgical accuracy	LCE < 22° or > 32°AI < 3° or > 13°Extrusion Index < 18% or > 28%Total femoral coverage < 72% or > 83%Anterior femoral coverage < 15%Posterior femoral coverage < 34%

Note. BMI, body mass index; LCE, lateral centre edge; AI, acetabular index.

Bernese periacetabular osteotomy (PAO)

The PAO is an accepted surgical technique for treatment of both hip dysplasia[78] and pincer-type FAI due to acetabular retroversion.[79] The aim of PAO surgery is to prevent or delay secondary osteoarthritis while improving hip biomechanics. In contrast to different pelvic osteotomies, the posterior column remains intact during PAO. This improves the stability of the reoriented acetabular fragment and facilitates postoperative rehabilitation at the same time. The birth canal remains intact and allows normal birth. The overall complication rate is relatively low considering the complexity of the surgery. The key point for a successful long-term outcome is an optimal reorientation of the acetabulum avoiding under- or over-correction for both hip dysplasia[80] and acetabular retroversion.[81] For the treatment of acetabular retroversion with anteverting PAO, a 10-year total hip arthroplasty (THA)-free survival of 100% has been described.[81] In addition, when comparing PAO and acetabular rim trimming for the treatment of acetabular retroversion, the first exhibited a higher long-term survival rate.[82] With optimal reorientation and a spherical femoral head, the cumulative survivorship of the hip after 10 years is 90.5%[80] for treatment of hip dysplasia. For the very first 75 patients, the cumulative THA-free survivorship at 20-year follow-up was 60%[83] and at 30-year follow-up was 43%.[84] The PAO has become the gold standard for the surgical therapy of hip dysplasia in adolescents and adult patients.

Although PAO is a rather complex operation, only few severe complications have been described so far (Table 4).In a recent review, analysing 4070 hips that underwent PAO, a complication rate of 7% was described.[85] Reduced complication rates were described for minimally invasive approaches.[85] Comparison between the studies remains difficult because of the heterogeneity of the studies and inconsistent training of the surgeons. A higher complication rate was described for patients with a BMI > 30.[86] The most common complications were transient or permanent damage of the lateral femoral cutaneous nerve with a prevalence of up to 30%,[87] asymptomatic heterotopic ossification being the most common Grade I/II complication with a prevalence of 20%[88] and protracted union with a prevalence of up to 15% (Fig. 6).[78,89] The most common complication requiring revision surgery was intraarticular osteotomy, with a prevalence of 1–15.5%.[90,91] Complications could be reduced with growing experience and the learning curve.[92] The reported prevalence of over-/under-correction is 22% while the LCE angle was more often under-corrected than over-corrected (20% versus 2%).[93] Hips with more severe dysplasia preoperatively were at higher risk for under-correction assessed with the LCE angle.[93] The prevalence of over-/under-correction was probably underestimated before the description of FAI.

Table 4.

Complications of periacetabular osteotomy (PAO) are listed below, with grading according to Sink et al.[118]

Grade	Complication	Prevalence	Reference
1 Complication without clinical relevance	Urinary tract infection	1.5–13%	[87,89]
	Superficial wound infection	5%	[136]
	Heterotopic ossifications Grade 1–2 (Brooker)	1.8–15%	[87,137]
	Postoperative fever	18%	[87]
2 Complication with outpatient or medication treatment	Paresthesia N. cutaneus femoris lateralis	30%	[87]
	Paresis N. femoralis	1.6–5.6%	[90,138]
	Paresis N. ischiadicus	1.5–7%	[89,90]
	Blood loss (> 5 blood conserves administered)	3–8%	[87,89]
	Avulsion of spina iliaca anterior superior	23%	[139]
	Deep wound infection	3–15%	[87,89]
	Discontinuity of the posterior column	1.5–8.5%	[87,89]
	Fracture of the os ischium	4.3%	[90]
	Stress fracture ramus inferior os pubis	5%	[136]
	Protracted union of osteotomies	2.6–15%	[78,89]
	Nonunion ramus superior os pubis, without revision surgery	6–16%	[89,136]
3 Complication with surgical therapy or unplanned hospitalization	Deep vein thrombosis, pulmonary embolism	3%	[89]
	Migration of the acetabular fragment	1.3–5.6%	[78,90]
	Heterotopic ossifications Grade 3–4 (Brooker) with surgery	1–8.5%	[90,91]
	Revision surgery for nonunion of the ramus superior os pubis	1%	[136]
	Revision surgery for haematoma evacuation	5%	[87]
	Intraarticular osteotomy or fracture	1–15.5%	[90,91]
4 Total hip arthroplasty or life-threatening complication	Necrosis of the acetabular fragment	4.2%	[90]

Fig. 6

(A) A 39-year-old patient with developmental dysplastic hip (lateral centre edge angle (LCE) of 15°) and preserved joint space. (B) Six weeks postoperatively following periacetabular osteotomy, LCE was 28°. (C) Anteroposterior pelvis view shows nonunion of the osteotomy and stress fracture of the inferior pubic ramus six months postoperatively. (D) A decortication and re-osteosynthesis was performed via ilioinguinal approach.

Theoretically, through over-correction during PAO, secondary hip impingement can be induced (Fig. 7). This can lead to iatrogenic acetabular retroversion[94] or pincer-type deformity, thereby reducing range of motion and requiring revision osteotomy.

Fig. 7

(A, B) A 41-year-old patient with history of Legg-Calvé-Perthes disease presenting with hip pain. Anteroposterior (AP) pelvis view and three-dimensional computerized tomography (3D CT) reconstruction show acetabular dysplasia with a prominent downsloping anterior inferior iliac spine (AIIS, white solid line) and coxa breva and magna. The anterior acetabular wall (AW) is shown in red, the posterior acetabular wall (PW) in blue. (C, D) The patient underwent subsequent periacetabular osteotomy and surgical hip dislocation with relative femoral head lengthening and offset correction. Six months postoperative, the patient presents with persistent pain and limited range of motion. The postoperative X-ray (C) and 3D reconstructed CT (D) show increased acetabular retroversion (positive crossover sign) and pronounced projection of the AIIS (white solid line) leading to intra- and extraarticular impingement. (E) Postoperative image after decompression of the too prominent AIIS and rim trimming via ilioinguinal approach.

Failure to correct associated cam deformity probably had a higher prevalence before the description of FAI in 2003.[2] Currently this complication can be easily avoided with concomitant cam resection,[80] either with open capsulotomy or with concomitant hip arthroscopy. This is important because a non-spherical femoral head is associated with lower long-term survival. In the presence of a deformity of the proximal femur (valgus hip or increased femoral antetorsion), a concomitant proximal femoral osteotomy should be evaluated.[95,96] Up to 23% of patients with hip dysplasia had concomitant high femoral antetorsion (> 35°), in a recent prevalence study.[97]

Femoral torsion correction

Abnormal femoral torsion has been described as an additional possible reason for FAI. Increased or decreased femoral torsion can cause extraarticular hip impingement.[98] Increased femoral torsion can cause posterior extraarticular ischiofemoral impingement.[23] On the other hand, decreased femoral torsion can cause anterior extraarticular subspine hip impingement; this is even worse if combined with mixed-type FAI.[99] Surgical treatment consists of hip arthroscopy or surgical hip dislocation combined with proximal femoral osteotomies. Derotational femoral osteotomy is performed for hips with increased femoral torsion and vice versa. Few outcome studies have evaluated this treatment after the description of FAI in 2003.[2] Therefore, it is questionable whether the outcome and complications of studies before 2003 should be compared with today’s treatment. Outcomes of recently published case series analysing patients who underwent femoral derotation osteotomy showed good clinical outcome.[95,96,100] Most of the patients reported that they would undergo surgery again.[96] However, for the treatment of decreased femoral torsion, usually hip arthroscopy with cam resection was performed. Some authors reported inferior outcomes of patients with decreased femoral torsion compared to patients with normal femoral torsion.[101] Therefore, some authors reported that decreased femoral torsion or femoral retrotorsion should be regarded as a contraindication for hip arthroscopy. Others recommended evaluation of femoral rotational osteotomy for these patients.[102]

Complications associated with the treatment of patients with torsional deformities of the femur depend on the treatment. The most common revision surgery after closed treatment with an intramedullary nail, is hardware removal.[95] Hardware removal was performed in the majority of patients in a recent case series of 55 femoral derotational osteotomies.[95] A nonunion rate of 2% and an infection rate of 2% were reported, while 4% underwent THA.[95] After open surgical treatment, the most common complication requiring revision surgery was also implant removal. Nonunion of the proximal femoral osteotomy ranged from 0% to 7%.[96,100] Previous studies reported nonunion rates of up to 15%, mostly for children.[103] Complications after open femoral derotation osteotomy are listed in Table 5. Next to hardware removal, subsequent surgeries included hip arthroscopy for adhesiolysis[96] or implant exchange due to implant failure.[100]

Table 5.

Complications of femoral derotational osteotomy, with grading according to Sink et al.[118]

Complication	Grade	Prevalence	Reference
Nonunion of the femoral osteotomy	III	0–7%	[100]
Deep wound infection	III	2%	[95]
Total hip arthroplasty	IV	0–4%	[95,96]
Intraarticular adhesions requiring adhesiolysis	II	12%	[96]
Hardware removal	–	64–71%	[95,96]

No predictive factors associated with failures are described in the orthopaedic literature. Tönnis and Heinecke described in 1999, that various types of femoral osteotomies result in improved clinical outcome,[102] unfortunately they did not report on complications associated with these procedures. For femoral rotational osteotomies to correct decreased femoral torsion, Tönnis and Heinecke reported less hip pain and balanced range of motion postoperative.[102]

SCFE – modified Dunn, pinning

Slipped capital femoral epiphysis (SCFE) is a long-known hip deformity of adolescent patients. Several classifications have been described previously, among them the classification of severity described Wilson (mild/moderate/severe)[104] while Loder[105] classified them based on stability (stable/unstable) of SCFE. Untreated SCFE can result in early osteoarthritis, hip pain and THA at young age.[106,107] Therefore, different surgical treatments have been performed. In situ pinning is probably the most common treatment for SCFE. Open surgery includes proximal femoral osteotomies and the modified Dunn procedure. This procedure allows anatomical restoration and normalization of hip function but is a difficult surgery. Long-term studies after the modified Dunn procedure showed no or only minimal signs of osteoarthritis.[67] Based on various studies on the vascular blood supply to the femoral head, the original technique according to Dunn had been modified. The modification included the development of a retinacular soft tissue flap containing the vascular blood supply to the femoral epiphysis.

According to a recent systematic review[108] analysing 58 studies with 2262 hips, the treatment of stable SCFE, in situ pinning using single screw had the lowest AVN rate of 1.4%. Overall, physeal osteotomy had the highest AVN rate of 11.1%. Physeal osteotomy exhibited the highest rate of chondrolysis of 9.8%. The highest rate of secondary hip impingement (FAI) was noted in patients with stable SCFE who underwent in situ pinning using single screw (30%). Regarding the development of OA, the highest rate was described for epiphysiodesis (23%) and for in situ pinning using multiple spins (15%).

Analysing the outcome of patients with unstable SCFE, a recent systematic review[109] included 25 studies with 679 hips and found an overall AVN rate of 21%. The AVN rate varied between the interventions, varying from 33% from in situ pinning to 5% for open reduction and internal fixation. Further subgroup analysis showed different AVN rates for moderate and severe slips. Timing of surgery (intervention performed within 24 hours or later) remains an important prognostic factor in predicting AVN in these subgroups of SCFE.

Complications associated with treatment of SCFE depend on the treatment approach. Although the modified Dunn procedure is a complex surgery, low rates of AVN were described in Europe. On the other hand, some authors in the US reported a high AVN rate, ranging up to 29% for unstable SCFE (Fig. 8).[110] An overall complication rate needing revision surgery was described between 7% and 15% but remains difficult because of the heterogeneity of the included patients.[111-114] Some authors performed the modified Dunn procedure exclusively for severe or unstable SCFE. While others performed this procedure for moderate and severe SCFE or for both stable and unstable SCFE. Subsequent surgery for improvement of secondary deformities and impingement ranged from 0% to 16%.[111,112,114-117] In Tables 6 and 7 the complications described in the literature are listed in the order of severity according to the classification of Sink.[118] In situ pinning, proximal femoral osteotomies and the modified Dunn procedure are associated with long-term survival. The challenge for the surgeon is the patient selection for open surgery and its treatment.

Fig. 8

(A, B) A 14-year-old boy presenting with hip pain and unstable moderate slipped capital femoral epiphysis (Southwick angle 43° shown in B). (C, D) Magnetic resonance imaging was performed showing joint effusion and bone marrow oedema at the femoral neck but no signs of femoral head necrosis. (E) Postoperative anteroposterior pelvis view six weeks after modified Dunn procedure. (F) Four months postoperative, patient presents with increased pain and radiographic signs of flattening femoral head indicative for avascular necrosis of the femoral head.

Table 6.

Complications of different treatments for stable slipped capital femoral epiphysis (SCFE) according to the review by Naseem et al,[108] with grading according to Sink et al.[118]

Complication	Grade	Treatment	Prevalence
AVN	III	Epiphysiodesis	3%
		in situ pinning using single screw	1.4%
		in situ pinning using multiple pins	2.2%
		Physeal osteotomy	11.1%
		Surgical dislocation	3.1%
FAI	III	Epiphysiodesis	NR
		in situ pinning using single screw	29.8%
		in situ pinning using multiple pins	NR
		Physeal osteotomy	1.5%
		Surgical dislocation	6%
OA	III/IV	Epiphysiodesis	23.3%
		in situ pinning using single screw	3.1%
		in situ pinning using multiple pins	15%
		Physeal osteotomy	12.2%
		Surgical dislocation	0%

Note. AVN, avascular necrosis of the femoral head; FAI, femoroacetabular impingement; OA, osteoarthritis; NR, not reported.

Table 7.

Complications of different treatments for unstable slipped capital femoral epiphysis (SCFE) according to the review by Alshryda et al,[109] with grading according to Sink et al.[118]

Complication	Grade	Treatment	Prevalence
AVN	III	in situ pinning	33%
		Epiphysiodesis	9%
		Closed reduction and pinning	26%
		Open reduction and internal fixation	5%
		Open reduction and physeal osteotomy	17%
		Surgical dislocation	18%

Note. AVN, avascular necrosis of the femoral head.

Conclusion

Preoperative evaluation and surgical planning are essential steps in joint preserving surgery. The choice of treatment method is crucial to approach the patient-specific pathomorphology and prevent surgical-related secondary problems such as instability and surgically induced FAI.