An evidence-based update on the management of articular cartilage defects in the hip

Abstract

Objective

Articular cartilage defects in the hip joint pose a significant surgical challenge and remain one of the most important determinants of success following arthroscopic intervention of the hip. The aim of this literature review was to report on the best available evidence on the various treatment options utilised for articular cartilage defects in the hip.

Material and methods

A comprehensive literature search was performed on PubMed from its inception to October 2021 using the following search strategy: ((hip) and (cartilage or chondral) and (repair or regeneration or restoration or implantation or chondroplasty or chondrogenic)). Two reviewers (KHSK, MG) independently reviewed titles and abstracts to identify articles for the final analysis. Articles were included if they were original research studies (randomised control trials, cohort studies, case-control studies, or comparative studies) on treatment of hip cartilage defects in humans reporting on a minimum of 5 patients. A total of 1172 articles were identified from the initial literature search. Following a thorough selection process, 35 articles were included in the final analysis to synthesise the evidence.

Results

Debridement, microfracture, autologous chondocyte implanatation (ACI) and matrix-induced ACI (MACI) are shown to have good short-to medium-term results. Injectable ACI and MACI have been developed to enable these procedures to be performed via arthroscopic surgery to reduce the post-operative morbidity associated with surgery with promising early results. Large cartilage defects which involved the sub-chondral bone may need the use of osteochondral grafts either autograft or allograft. Newer biological solutions have been developed to potentially deliver a single-stage procedure for hip cartilage injuries but longer-term results are still awaited.

Conclusion

Accurate identification of the extent of the injury helps stratify the defect and plan appropriate treatment. Several surgical techniques have shown good short to medium-term outcomes with ACI, AMIC, mosaicplasty and microfracture. Recent advances have enabled the use of injectable MACI and bioscaffolds which show promising results but in the shorter term. However, one needs to be mindful of the techniques which can be used in their surgical setting with the available resources. In order to thoroughly evaluate the benefits of the different surgical techniques for hip cartilage defects, large scale prospective multi-centre studies are necessary. Perhaps inclusion of such procedures in registries may also yield meaningful and pragmatic results.

1. Introduction

Articular cartilage defects in the hip joint pose a challenge to obtain successful outcome.¹ They often lead to significant pain and disability.¹ They can occur as a result of abnormal hip joint morphology or acquired conditions. Femoroacetabular impingement (FAI) and developmental dysplasia of the hip (DDH) are the most common morphological abnormalities in the hip joint. On the other hand, acquired conditions comprise of osteonecrosis, osteochondritis dissecans, slipped capital femoral epiphysis (SCFE) or trauma to name a few.² Isolated cartilage injuries in the hip joint present a technical challenge largely due to their location.² Accurate characterisation of the chondral lesion is imperative to institute appropriate treatment, and therefore an accurate and prompt diagnosis of articular cartilage damage is essential to successfully treat the pathology.³

Thorough pre-operative investigations using appropriate imaging modalities provide useful information to diagnose chondral lesions and plan treatment.^4,5 Plain radiographs provides valuable information regarding the bone morphology and any gross arthritic changes. Magnetic resonance imaging (MRI) provides a good assessment of the extent of chondral injury.^1,5 Contrast medium can be used as an adjunct with MRI to provide more detail of the intra-articular structures. Computed tomography (CT) scan is useful to characterise bony abnormalities such as cam and pincer deformities with added advantage of assessment of quantifying joint space narrowing.^1,5 3D reconstruction of the CT scan is useful to further assess the morphological abnormalities of the hip joint.^1,5

Chondral injuries can be classified depending on the severity using one of the various available classification systems. Some commonly used classification systems are shown in Table 1, Table 2.6, 7, 8, 9, 10, 11 Even though recent advances in imaging modalities can identify and grade the severity of the cartilage injuries, accurate classification of the severity of the cartilage lesion can only be possible at the time of surgery. Accurate assessment and documentation of the cartilage lesions is essential to first plan the appropriate treatment. In addition, accurate documentation helps to monitor the outcome and is useful to compare outcomes between different centres as a part of research studies or larger registry based studies. Table 3 shows a commonly used system to classify the articular cartilage defects of the hip as seen at hip arthroscopy.¹² Finally, a geographic zone method has been described (Fig. 1, Fig. 2) by Ilizaliturri et al. to further characterise the location of intra-articular pathology observed at hip arthroscopy.¹³ The classifications systems described in Table 3 and Fig. 1 are utilised by the Non-Arthroplasty Hip Registry (NAHR) in the UK.¹⁴

Table 1.

Classification of Cartilage defects using different systems.

Outerbridge Classification8		ICRS Classification9		Beck Classification6,7
0	Normal	0	Normal	0	Normal	Cartilage intact on macroscopic examination
1	Softening and swelling of the cartilage	1	Nearly normal: superficial lesion	1	Malacia	Fibrillation or roughened cartilage surface
2	Partial-thickness lesion, diameter <0.5 inch	2	Abnormal: lesions <50% of cartilage depth	2	Debonding	Cartilage intact but separated from sub-chondral bone
3	Partial-thickness lesion, diameter >0.5 inch	3	Severely abnormal: lesions >50% of cartilage depth	3	Cleavage	Cartilage separate from sub-chondral bone with frayed edges or thinning
4	Full thickness lesion down to subchondral bone	4	Severely abnormal: lesions through subchondral bone	4	Defect	Full thickness cartilage defect

Table 2.

Classification system described by described by Buckwalter.^10,11

Classification of chondral and osteochondral injuries
1	No visible disruption of the articular surface Internal chondral damage and subchondral bone injury
2	Mechanical disruption of the articular surface limited to articular cartilage
3	Mechanical disruption of articular cartilage and subchondral bone

Table 3.

Classification of acetabular chondral defects identified at arthroscopy.¹²

Severity
1	Wave Sign – detachment from sub-chondral bone Intact chondrolabral junction
2	Chondrolabral junction separation but no delamination; Cleavage tear
3	Delamination – macroscopic debonding of cartilage from acetabular bone
4	Exposed bone
Extent – Grades 1, 3 and 4 further classified into A, B and C This takes in to account of the distance of the lesion from the rim of the cotyloid fossa
A	Lesion less than one-third of the distance from the acetabular rim to the cotyloid fossa
B	One-third to two-thirds of the distance from the acetabular rim to the cotyloid fossa
C	Greater than two-thirds of the distance from the acetabular rim to the cotyloid fossa

Fig. 1.

Geographic zones of the acetabulum (left hip is shown in the figure).¹³

The acetabulum is divided into 6 zones by two vertical lines on either side of the cotyloid fossa and a horizontal line through the centre of the acetabulum. PS – posterosuperior; PI – posteroinferior; AS – anterosuperior; AI – anteroinferior.

Fig. 2.

Geographical zones of the femoral head which corresponding to the acetabular geographic zones.¹³ Zones 2, 3 and 4 are further sub-divided into 3 areas corresponding to 1/3rd of the area: M − medial, S – superior and L – lateral.

A recent systematic review by the senior author (VK), showed several different techniques are available to treat cartilage injuries of the hip joint (Table 4).² The aim of this literature review was to report the best available evidence on the various treatment options for hip cartilage defects.

Table 4.

Different techniques available to treat cartilage injuries in the hip joint as described by Nakano et al.²

	Procedure
1.	Debridement
2.	Microfracture
3.	Autologous chondrocyte implantation (ACI)
4.	Matrix-induced autologus chondrocyte implantation (MACI)
5.	Autologous matrix-induced chondrogenesis (AMIC)
6.	Osteochondral autograft transplantation
7.	Osteochondral allograft transplantation
8.	Direct cartilage suture repair
9.	Fibrin adhesive
10.	Intra-articular bone marrow mesenchymal stem cells (BM-MSC) injection
11.	Artificial plug (TruFit®)

2. Methods

A comprehensive literature search was performed on PubMed from its inception to October 5, 2021. The search was performed using the following keywords with the Boolean operators - ((hip) and (cartilage or chondral) and (repair or regeneration or restoration or implantation or chondroplasty or chondrogenic)). The inclusion and exclusion criteria for the review were decided a priori by the two authors performing the review (KHSK and MG). Articles were included if they were original research studies (randomised control trials, cohort studies, case-control studies, or comparative studies) on treatment of hip cartilage defects in humans reporting on a minimum of 5 patients. The articles were limited to only English language and only those looking at hip joint pathology. Articles were excluded if they were review articles, editorials, had less than 5 patients, reported on other joints – knee, shoulder, elbow, ankle etc or were animal experiments. References of the full text article selected for review were searched to identify any other relevant article to be included for the final analysis. After title and abstract screening, full-text articles of potentially eligible studies were obtained and reviewed against inclusion and exclusion criteria. The PRISMA flowchart for the screening process in shown in Fig. 3.

Fig. 3.

PRISMA flowchart for the screening process.

2.1. Data management

The articles were imported into the Rayyan reference management software (https://www.rayyan.ai/) to aid selection and screening.¹⁵

2.2. Selection process

A thorough selection process was followed to identify the articles for final analysis. Two reviewers (KHSK, MG) independently reviewed titles and abstracts to identify articles for the final analysis. This two-stage process was strictly followed by the two authors independently to conclude on the final articles. Any discrepancy was resolved by discussion between the two at each stage of selection process. In case of disagreement, the senior author (VK) was consulted to reach a consensus.

3. Results

A total of 1172 articles were identified on the initial search on PubMed. Of these 35 articles which reported the clinical results of the treatment strategy for hip cartilage defects with a minimum of 5 patients were included. The following section summarises the best available evidence for each of the technique used for the treatment of hip cartilage defects.

3.1. Debridement

Debridement of the articular cartilage flap helps to improve symptoms such as pain and restriction of activities.¹⁶ Debridement has been used commonly for knee cartilage defects and is suitable for superficial cartilage injuries which can be removed to ensure a stable edge. Commonly this is performed using a soft tissue shaver, but a radiofrequency probe can also be used with the procedure being termed as coblation chondroplasty. Debridement has a role in the management of superficial cartilage defects and has shown to improve symptoms. Fontana et al. showed inferior outcome for isolated debridement when compared to those who underwent ACI in their retrospective case control study comparing on ACI versus debridement for Outerbridge grades 3–4 traumatic chondral defects measuring more than 2 cm².¹⁷ The paucity of studies on debridement or chondroplasty may in fact be due the fact that other treatment strategies are being utilised or perhaps due to the debridement being performed in conjunction with other intra-articular procedures being utilised to treat labral pathology.

3.2. Microfracture

Microfracture was originally developed to treat knee cartilage defects.^18,19 Current literature supports microfracture in the short term with good to excellent results for small defects (</ = 2–4 cm²).17, 18, 19, 20 Microfracture involves making multiple drill holes through the sub-chondral bone to allow the formation of a clot at the site of cartilage defect. The clot potentially has some mesenchymal stem cells which in turn help with formation of cartilage.17, 18, 19, 20 The resultant cartilage from microfracture is fibrocartilage whose biomechanical properties are inferior to hyaline cartilage.

Microfracture is a widely used technique for hip chondral injuries with several authors reporting good outcomes. Philippon et al. reported promising results with microfracture in 89% of patients at a mean of 20 months.²¹ The article reported a minimum of 95% coverage for cartilage defects treated with microfracture. Similarly, Karthikeyan et al. reported a mean fill of 96% of the defect at a mean follow-up of 17 months in 95% of patients treated with microfracture.²² Furthermore, Zaltz et al. in their small case series of seven patients who underwent microfracture after surgical dislocation of the hip showed good outcomes. Six out of these seven patients returned to their baseline pre-operative functional level. The one patient who did not improve had a problem in the contralateral hip.²³ On the contrary, Hevesi et al. in their series of 110 patients treated with debridement (n-82) and microfracture (n = 31) reported similar results between both the procedures, supporting debridement over microfracture.²⁴

3.3. Autologous chondrocyte implantation (ACI)

ACI was first reported to have good outcome for treating large (2–10 cm²) cartilage defects in the knee by Brittberg in 1994.²⁵ Over the last two decades, positive results are seen with ACI in the treatment of knee cartilage defect but there are very few studies on the usefulness of ACI in the hip. ACI is performed in two-stages. The first procedure involves harvesting autologous chondrocytes from a donor site which are then cultured, and chondrocytes multiplied several-fold prior to the chondrocytes being re-implanted into the affected area of the cartilage defect.²⁵ The gap between the two procedures is around 11–21 days during which the harvested chondrocytes are multiplied to obtain around 2.5 to 5 million cells. During the second stage procedure, the chondrocytes which are cultured in the laboratory, are implanted into the defect, which is covered by either a collagen scaffold or periosteum. Fontana et al. reported a better final Harris Hip Score (HHS) for patients who underwent ACI when compared to debridement (HHS: ACI – 87.4 vs debridement – 56.3).¹⁷ However, Moriya et al. performed immunohistochemical analysis on four samples out of six patients who underwent ACI and found that the reparative cartilage following ACI had less glycosaminoglycan concentrations in spite of a good clinical outcome,.²⁶ Recently there are reports of injectable ACI being performed via arthroscopic surgery in a small cohort of 13 patients showing a reduction in pain and improvement in patient reported activity level and quality of life.²⁷ Kruger et al. showed promising results after a minimum of 24 months in their series of 36 patients who underwent ACI for large acetabular cartilage defects.²⁸ In their series they found a complete defect fill in 87.5% of cases. In spite of these positive reports on the outcome of ACI in the short to medium term, there is still a lack of large-scale studies supporting the regular use of ACI for hip cartilage defects with long-term benefits.

3.4. Matrix-induced autologous chondrocyte implantation (MACI)

MACI is a second-generation ACI technique. Here the cultured chondrocytes are implanted onto absorbable scaffolds. These scaffolds are then transplanted onto the cartilage defect at the second stage. MACI can be performed via arthroscopic surgery thereby reducing the morbidity associated with open surgical procedures. Mancini et al. reported an improvement in the modified Harris Hip Score (mHHS) at six months follow-up which continued to improve up to three years post-operatively, following both MACI and AMIC.²⁹ Similarly, Kvorsmeier et al. and Fickert et al. reported on sixteen patients and six patients respectively who underwent MACI and concluded that MACI was a feasible option for full thickness cartilage defects in the short term.^30,31 Several authors have reported on the use of injectable MACI for the treatment of acetabular chondral defects. Schroeder et al. in their series of 20 patients showed significant improvement in mHHS to 93 and iHOT-33 to 79 when compared to pre-operative scores.³² Similar improvement in post-operative mHHS (64–91) and iHOT-33 (44%–86%) was reported by Krueger et al. in their series of 32 patients.²⁸ Furthermore, Bretschneider et al. and Thier et al. reported similar improvement in activity level, quality of life and reduction of pain following the use of MACI in their series.^27,33

3.5. Autologous matrix-induced chondrogenesis (AMIC)

AMIC is a one-stage procedure to treat cartilage defects. Here a collagen matrix patch is used to cover the cartilage defect after a standard microfracture procedure. The collagen patch helps stabilise the fibrin clot and provides a stable environment for the clot to form cartilage. Current literature shows promising results with AMIC at short to medium term follow-up.²⁹ Leunig et al. showed short-term improvement in Oxford Hip and UCLA scores with AMIC in their series of six patient at a 1 year follow up.³⁴ Fontana et al. in a large series of 201 patients reported a significant improvement of mHHS in patients treated with AMIC for Outerbridge grade III or IV chondral lesions of the acetabulum.³⁵ The improvement was seen at six months post-operatively which continued up to three years,³⁵ Furthermore, Fontana et al. showed that AMIC (N = 70) resulted in a superior outcome compared to microfracture (N = 77) with sustained benefit in the medium term whereas those who underwent microfracture slowly deteriorated after four years.³⁶ Similar improvement in the mHHS following AMIC was reported by de Girolamo et al. at the 8 year follow-up.³⁷ Advances in technology have made it possible to use a liquid acellular collagen matrix for the treatment of cartilage defects. De Lucas Villarrubia et al. have shown liquid AMIC is a safe procedure and the 25 patients in their series showed improvement in mHHS, VAS for pain and satisfaction level at the 29 month follow-up.³⁸

3.6. Osteochondral autograft transplantation (Mosaicplasty)

Large cartilage defects which involve the subchondral bone will not be amenable to the procedures described above. To treat such large defects, mosaicplasty was devised wherein healthy mature cartilage from non-weight bearing part of the knee or hip is harvested and transplanted to the cartilage defect. This procedure has the advantage of the bone plug incorporating into the recipient site bone. The gap between the transplanted cartilage and the recipient cartilage surface is gradually filled in with freshly formed fibrocartilage.³⁹ Girard et al. reported complete incorporation of the autograft bone plugs in a series of patients (n = 10) who underwent mosaicplasty for femoral head cartilage defects.⁴⁰ In addition, at a mean follow up of 29.2 months there was significant improvement in Merle d’Aubignue Postel score and an improvement in hip range of movement.⁴⁰ Similarly, Viamont-Guerra et al. reported improvement in mHHS (56.3–88.4) and WOMAC score (45.1–80.6) following mosaicplasty at 12 months in their series of 22 patients.⁴¹ However, Hanke et al. reported a modest 57.1% survivorship at five years in their series of twelve patients who underwent mosaicplasty for femoral head impaction defects following traumatic hip dislocations.⁴²

3.7. Osteochondral allograft transplantation

For larger cartilage defects requiring osteochondral grafts one may have to consider the use of allografts. Osteochondral allografts have the advantage of providing a large cartilage surface which can be accurately prepared to fit the defect with the added advantage of having an immediately functional hyaline cartilage without the risk of donor site morbidity. However, this procedure is expensive with an additional need to match the recipient to the donor tissue.

Khanna et al. in their prospective study on seventeen patients who underwent osteochondral allograft transplantation showed that 13 patients reported significantly better mHHS score at a mean of 41.6 months.⁴³ The remaining 4 patients had further surgical procedures due to failure of the graft. Similar results were reported by Mei et al. in their series of 22 patients, where the mHHS improved from 48.9 to 77.4 at a mean follow-up of 68.8 months.⁴⁴ Five patients underwent conversion to total hip arthroplasty, resulting in a survivorship of 67.5% at 9 years.⁴⁴ Furthermore, Oladeji et al. reported that 70% (7/10) of patients had successful functional outcomes following this procedure.⁴⁵

3.8. Direct cartilage suture repair

Direct cartilage repair is a technique which can be used to treat large delaminated full-thickness acetabular cartilage injury. In such cases the acetabular cartilage separates from the underlying subchondral bone. Direct cartilage repair is an option but in practise this may not always be possible due to the nature of the chondral flap. We did not identify any articles reporting on the clinical results which satisfied our inclusion criteria.

3.9. Fibrin adhesive

Isolated full thickness cartilage flaps may be amenable to complete preservation in early stages. In such cases, the chondral flap is usually lifted and perhaps in the early stages be identified at arthroscopy as a wave sign. A peripheral incision on the chondral flap allows the flap to be lifted and perform microfracture on the sub-chondral bone. Following the microfracture the chondral flap is then replaced and sealed with fibrin glue. The cartilage is then pressed down to allow for bonding between the cartilage flap and sub-chondral bone. Tzaveas et al. reported a significant improvement in their series of 19 patients.⁴⁶ Furthermore, Stafford et al. from the same group reported on 54 patients who underwent this procedure (19 of whom were reported previously by Tzaveas et al.) and found that mid-term results were promising.⁴⁶

3.10. Intra-articular bone marrow mesenchymal stem cells (BM-MSC) injection

Mesenchymal stem cells (MSCs) are the focus of several researchers looking for the ideal treatment for articular cartilage defect due to their inherent potential to differentiate into various tissues, including cartilage. Mardones et al. reported significant improvement of mHHS, WOMAV and VAIL scores from 64.3, 73 and 56.5 to 91, 97 and 83 respectively at final follow up in 29 hips.⁴⁷ The BM-MSCs were given in three intra-articular injections at four to six weeks interval. The procedure was found to be safe with no complications at 2 year follow-up.⁴⁷

3.11. Artificial plug (TruFit®)

TruFit cartilage/bone plug (Smith & Nephew) is a resorbable polymer scaffold that can be inserted into osteochondral defects. It helps in articular cartilage regeneration by providing a suitable environment to promote bone growth by facilitating the bone marrow cells to migrate into the plug.⁴⁸ Again, we did not identify any articles reporting on the outcomes of this procedure which satisfied our inclusion criteria.

3.12. Bioscaffold

BST-Cargel (Smith & Nephew) is bioscaffold formed by mixing the product, a chitosan solution with the patient's blood. This forms scaffold which can then be applied over the microfracture site to stimulate the bone marrow.⁴⁹ Rhee et al. reported improvement in patient reported outcome measures with BST-Cargel for large chondral defects at 1 year in their cohort of 37 patients. Tahoun et al. showed that 91% of patients who underwent BST-Cargel maintained satisfactory clinical outcome at 2 years following the procedure.⁵⁰ In addition, Tahoun et al. further characterised the repair tissue on T2 mapping and found that the tissue was similar to native joint cartilage.⁵¹ The procedure resulted in more than 90% filling of the cartilage defects.⁵² Furthermore, John et al. in their study comparing BST-Cargel versus microfracture alone, demonstrated that BST-Cargel bioscaffold had good early results at two years with maintaining the joint space and delaying the conversion to total hip arthroplasty.⁵³

4. Conclusion

Chondral injuries in the hip are a major cause of pain and disability especially in the young adult. Accurate identification of the extent of injury can help stratify the defect and plan appropriate management. Several surgical techniques have shown improvement in short-to medium-term outcomes with several authors reporting on ACI, AMIC, mosaicplasty and microfracture. Recent advances in technology have enabled the use of injectable MACI and bioscaffolds which show promising results but in the short term. However, one needs to be mindful of the techniques which can be used in their surgical setting with the available resources. Appropriate training in the surgical techniques is essential to achieve excellent results. Finally, we noticed a significant amount of heterogeneity in terms of usage of the classification systems to characterise the lesion and a number of different outcome measures in reporting the outcomes of different interventions. It is essential that international bodies like ISHA take the initiative to help standardise the classification system to be utilised for cartilage defects and also the outcome measures. Furthermore, large scale prospective multi-centre studies are necessary to thoroughly evaluate the benefits of the different surgical techniques for hip cartilage defects.

Authors contribution

KHSK – Conception, design, literature search, writing of manuscript and editing.

MG – Literature search and approval of manuscript.

VK – Conception, design, methodology and editing of manuscript.

Statement

This article was exempt from ethical approval. No funding was received for this project.

Financial disclosures

KHSK - None.

MG - None.

VK – Has received research grants from JRI and Pfizer and is an educational consultant for Smith & Nephew and Arthrex.

Declaration of competing interest

None.