In this study, we performed a retrospective analysis of 21 patients with SC who underwent arthroscopy surgery. All but 1 patients have thus far reported a good outcome, with a pain-free joint, functional range of motion, and return to their normal activities of daily living (including sport). Upon review of these cases, certain phenomenon deserved extra attention to be paid to.
Milgram classified loose bodies of SC into three types3: type Ⅰ or early stage, where there are synovial-based masses without intra-articular loose bodies; type Ⅱ or intermediate stage, where there are synovial-based masses and free intra-articular bodies; and type Ⅲ or late stage, with multiple free osteochondral loose bodies without demonstrable synovial disease. In our study, six additional wedged-clump type were found besides three types described by Milgram (Table 4). They appeared to be aggregation of loose bodies wedged, compressed and accumulated at the horseshoe fossa, shaping like pomegranate seeds, makes it difficult to be observed (Fig. 4D). There’s no entanglement between loose bodies and synovium, distinct them from Milgram type Ⅱ or intermediate stage. The authors believe that the unique morphology of wedged-clump type loose bodies were due to the specific enarthrodial anatomy and biomechanical structure. Constant compression from femoral head wedged numerous small loose bodies into the acetabulum fossa and forged these into a whole big clump. Therefore, as a classification designed for SC of all joints, Milgram’s theory doesn’t classified these as a separate category. Many physicians have described the large clumps of loose bodies formed by smaller ones and lodged into the acetabulum fossa 7; 15–18, proving its universal existence. We believe that this type of loose bodies distinguish themselves in terms of radiographic appearance, arthroscopic morphology and surgical strategy to deal with. Therefore, we conclude our findings and hope it will provide certain guidance for fellow physicians.
Table 4
| Milgram stage I | Milgram stage II | Milgram stage III | Wedged-clump type |
Male | 2 (9.5) | 1 (4.8) | 4 (19) | 4 (19) |
Female | 1 (4.8) | 2 (9.5) | 5 (23.8) | 2 (9.5) |
Total | 3 (14.3) | 3 (14.3) | 9 (42.9) | 6 (28.6) |
SC’s tendency of recurrence and 5% of malignant transformation to synovial chondrosarcoma or chondrosarcoma makes it cannot be neglected19 20; 21. Due to the non-specific symptoms, the diagnosis of hip SC largely depends on radiographic findings. However, plain radiographs show the presence of loose bodies in only 50% of the cases22, as 1/5 ~ 1/3 of loose bodies were not ossified23; 24, making it notoriously elusive in imaging studies. In our study, loose bodies were detected in most cases on plain radiograph, with only three cases of negative finding. We conclude the relatively high resolution to the late stage development of most cases, which is corresponded with the arthroscopic findings. Most patients were reluctant to undergo any surgical management without actual evidence of pathological change until the symptoms became intolerable or radiopaque intra-articular loose bodies became ossified and visible on radiograph, which resulted in irreversible damage to the joint and consequently unsatisfying prognosis. MRI has become international gold standard in imaging SC in the pre-mineralization phase. Being a synovial pathology, morphologic changes are demonstrated best by contrast-enhanced T1-weighted fat suppressed, axial T2-weighted and coronal T1-weighted sequences25.As for the smaller loose body, MRI only presented as hip hydrops26. An atypical radiological appearance was identified on plain radiograph of three patients with wedged-clump type loose bodies (Fig. 5). It’s very similar to the image appearance of OCD (Osteochondritis dissecans) with large piece of ossified fragment dislodged from acetabulum and fell into the joint space. Both the shape of wedged-clump type loose bodies and OCD fragment were found to be fitting the contour of the acetabulum, making them indistinguishable radiographically. Differential diagnosis between these two conditions were ambiguous, as neither symptoms nor radiological manifestation were specific. Arthroscopic surgery could serve as both treatment and diagnostic tool in this dilemma. In our study, three cases of the six wedged-clump type presented with large ossified fragment fitting the concavity of acetabulum. Small amount of independent loose bodies were found in the central and peripheral compartment under arthroscopic inspection. We believe that the relatively smaller quantity of scattered loose bodies was due to the fact that most loose bodies were compressed into the acetabular fossa and forged into one big clump. These additional small ossified loose bodies could be an indication for the diagnosis of SC, but were sometimes invisible on plain radiograph due to their insidious location or non-ossified status.
Different strategies were applied according to different types of loose bodies. Type Ⅰ (Fig. 4A) was characterized by loose bodies confined in the synovium. At this stage, synovium remains its chondromateplastic potential, so the authors believe that a total synovectomy is essential to avoid recurrence and achieve a better prognosis. Loose bodies should be carefully searched and clamped out before synovectomy. Extra caution needs to be taken as to not break free and lost track of the loose bodies to reside intra-articularly when performing synovectomy. In type Ⅱ (Fig. 4B), some “loose bodies” were not loosen any more. They were located at and attached to the free side of the synovium, making them generally hard to miss. Loose bodies should be taken care of at first, and then other pathological conditions. In our opinion, synovium should also be completely resected at this stage to prevent postoperative recurrence. In type Ⅲ (Fig. 4C), scattered loose bodies were not confined in a specific area and moving freely in the joint capsule. The shape of loose body varies from round, oval, rice-shaped to antlers, and so was the size. Flexing, extending and rotating of the hip joint after relaxation and traction during the operation can effectively avoid the missing of loose bodies. Observation of the lateral part of the hip was more accessible when hip was fully flexed and external rotated, which is relatively easy compared to the medial part, which could be best inspected with the hip extended and internal rotated. Following methods were taken to avoid blind angle: (1) Interchange the approach of arthroscopy and surgical instrument; (2) Using arthroscopy of 30° and 70° in turn; (3) Expanding the internal access of the approach to increase the range of the movement of scope. Synovectomy should be restricted to the hypertrophy and hyperemia area. When dealing with the wedged-clump type (Fig. 4D), due to the embedding of the loose bodies into the acetabular fossa, it’s difficult for the general surgical instruments to reach to. Curved scraper and slide winder blade were needed to remove all the loose bodies out. Some of the wedged big ones were in fact the aggregation of many small loose bodies hinged together, each with intact calcified or cartilaginous surface of its own. Clamping too hard may result in morselization of the aggregation and scatter of the floating loose bodies, increasing complexity and time duration of the surgery. However, when the wedged loose bodies were too big to maneuver, breaking down of the aggregation might be inevitable. A halfpipe cannula might be used to secure the easy passage of the small chipped loose bodies.
The precise congruency of the articulation of acetabulum and femoral head makes hip an intricate structure. Despite its relatively large size, the intra-articular space of hip joint for surgical maneuverability is relatively insufficient. T-shaped capsulotomy was first brought up by Horisberger et al27 for the management of FAI. It’s an incision between the ALA, AMA and DALA on capsule along the axis of femoral neck, along the iliofemoral ligament and perpendicular to the intertrochanteric line (Fig. 6). It aims to increase exposure for better arthroscopic surveillance of peripheral compartment and space for instrument operability to deal with certain central compartment pathology. In this study, it was carried out in each case to facilitate instrument maneuverability and thorough inspection of capsular recess. It allows the removal of loose bodies as many as possible and does not add substantially to the case time, complications, or complexity. Moreover, a complete exposure becomes more accessible with this cut and therefore result a more thorough synovectomy without taking the risk of a series of potential complications resulted by dislocation of hip joint. In addition to that, FAI is known for commonly associated with hip SC28; 29, along with labrum abrasion and tear. T-shaped capsulotomy facilitate not only the resection of osteophytes at the junction between femoral head and neck, but also debridement, stitches and suture anchor placement to manage the labral pathology.
It should be noted that the following problems still exist in this study: Limited number of cases were included in this study, and with a larger size of samples, the credibility will be more authoritative. Longer follow-up time is also needed for better credibility. We believe that our experience and operative guidance followed could help to achieve a more satisfactory outcome and to lower the rate of recurrence and other complications. Hopefully this theory could provide theoretical guidance and support for clinician to perform better diagnosis and treatment for patients.