Unusual case of mixed form of femoroacetabular impingement combined with nonspecific synovitis of the hip joint in a young adult – A case report

Introduction. Minimal bone changes in the acetabulum and/or proximal femur, through mechanism known as femoroacetabular impingement, during flexion, adduction and internal rotation lead to early contact between femoral head-neck junction and acetabular brim, in anterosuperior region. Each additional pathological substrate which further decreases specified clearance provokes earlier onset of femoroacetabular impingement symptoms. Case report. We presented a 20-year-old male patient with groin pain, limping, positive impingement test, radiological signs of mixed form of femoroacetabular impingement and unrecognized chronic hypertrophic synovitis with earlier development of clinical hip symptoms than it has been expected. Open surgery of the left hip was done. Two years after the surgery, patient was asymptomatic, painless, and free of motion, with stable x-rays. Conclusion. Hypertrophic synovial tissue further reduces the distance between the femoral head-neck junction and the acetabulum, leading to the earlier onset of femoroacetabular impingement symptoms. Surgical treatment is the method of choice.


Introduction
Acetabular labrum damage leads to loss of its function, early appearance of groin pain, loss of hip function and early hip osteoarthritis development 1,2 .Numerous pathomechanism have been proposed to explain the labrum damage, in-cluding the femoroacetabular impingement (FAI) 3,4 .Minimal bone changes of the acetabulum and/or femoral head, reduce the distance between them, leading to premature contact-impact of the femoral head-neck junction on the edge of the acetabulum, damaging labrum and labrum adjacent cartilage, wich are early signs of hip arthritis [5][6][7][8] .Three types of FAI have been described: the first one is cam type with a morphological changes at the femoral head-neck junction in the form of cam deformmity 9 .The secoond one is pincer type, in which the patological changes are localized exclusively to the acetabulum as a global (coxa profunda, protrusio acetabuli) or local overcoverage (retroversio acetabuli) of the femoral head, where the motion of the hip leads to the impact of the femoral neck on the edge of the acetabulum and consequent damage to the acetabular labrum 4 .The third, mixed and the most common type of FAI is the combination of the previous two 7, [10][11][12][13] .Synovitis of the hip is a reaction of the articular synovium on the systemic or local pathological substrate in the form of synovial joint fluid production [14][15][16] or specific hypertrofic synovium reaction that is seen in pathological conditions such as pigmented villonodular synovitis, tuberculosis or rheumatoid pannus [17][18][19][20] .In the literature we found no case of hypertrofic non-specific synovitis combined with any kind of FAI.
We presented a patient with nonspecific chronic hypertrofic synovitis of the hip, combined with a mixed form of FAI, who was surgically treated.

Case report
A 20-year-old male patient suffered from pain in the left groin, which lasted two years before the surgery.The patient was treated in several orthopedic institutions with non-steroid anti-inflammatory drugs, physiotherapy, skin traction, and suggested total hip replacement.Six months before the sur-gery, during the ultrasound examination of the hip joint, synovial fluid in the hip was asserted for which injection of corticosteroids into the joint was administered.After that, the symptoms became more pronounced, the patient began to limp visibly, walking on flat surfaces was difficult, and climbing up the stairs was practically impossible.At clinical examination the patient walked with the left leg in external rotation, with highlighted limps on that leg, Trendeleburg sign was positive on the left leg, highlighted weakness of muscles of the thigh and the left gluteal region, active flexion of the hip was possible up to 70°, internal rotation up to 5°, adduction up to 10° in the hip flexion of 70°.Impingement test was positive in the hip flexion of 30-70° 3 .The patient brought computed tomography (CT) image of the hips and nuclear magnetic resonance (NMR) that were made before the application of corticosteroids into the joint and which showed that the bone and soft tissue structures of the hips were normal.Biochemical and laboratory tests were also within normal limits.Standardized anteroposterior radiography of the hips showed characteristics findigns for femoroacetabular impingement reported earlic in literature: (Figure 1) a strong mutual retroversion of the acetabulum 12° on the left and 11° on the right hip 21 , mutual positive sign of ischial spine projection 22 , the angle α was 46° on the right and 44° on the left 23 , acetabular index, mutual 10° 24 , mutual Wiberg angle 36° 25 , a kolodyaphyseal angle of 126° that was asserted bilaterally.
In profile, Dunn-Ripstein-Müller's radiographs of the hips 26 , the angle α on the left was 64° (normal value of this angle is below 50°), and on the right 42° (Figure 2).Such clinical and radiographic findings revealed the existence of mixed-type of FAI on the left hip, due to which we proposed surgical treatment to the patient.The patient was operated on.It was planned to lift the acetabular labrum from its base, to osteotomize overcovered anterior and superior edge of the acetabulum, then, reinsert acetabular labrum in a new slot, and osteotomize cam deformity at the femoral head-neck junction in its antero-superior region.Lateral hip incision and transtrohanteric flip osteotomy of the hip were done 27 , and after anterior ''Z'' hip capsulotomy unexpected hypertrophic synovial hip reaction was aserted (Figure 3).

Fig. 3 -Intraoperative image: hypertrophied synovitis of the joint capsule on the anterior and superior femoral neck and head (black arrow), and femoral head (yelow arrow).
Entire extra-acetabular part of the joint was filled with synovial tissue which had fully and seriously damaged the anterior and the superior part of the acetabular labrum.Partial hip synoviectomy was performed, tissue samples were sent to histopathological analysis, the damaged parts of the labrum was resected, without possibility to be reinserted, anterior and superior part of the acetabular edge were osteotomized to reduce acetabular retroversion.Osteochondroplasty of the cam prominence at the femoral head-neck junction was done (Figure 4), and thus, intraoperatively, hip flexion of 90° and internal rotation of 30° was obtained 28 .After joint capsule reconstruction, osteotomized part of the greater trochanter was re-fixed with two cortical screws and the operational wound was closed.Postoperatively, the patient was reimbursed with 400 mL of blood; low molecular weight heparin thromboprophylaxis for seven days was introduced, followed by oral anticoagulant therapy for up to six weeks after the surgery.On the first postoperative day active exercises in bed started and walking on the crutches was allowed from the second day with touching the tip of toes of the operated leg for six weeks after the surgery.Histopathological findings confirmed a nonspecific chronic hypertrophic synovitis of the hip.Two years after the surgery, the patient was asymptomatic, without limping on the left leg and with normal life activities.Flexion of the operated hip was 90°, internal rotation 25°, adduction 30°, impingement test was negative.On the anteroposterior radiographs of the hips, the acetabular angle of retrovesion was reduced up to 4°, the angle α was 40° and 49° on the profile of Dunn-Rippsetin-Müller radiographs of the left hip.

Discussion
Damages of the acetabular labrum cause pain and partial loss of function of the hip in young adults.There is a number of reasons for labrum lesions, such as mechanical trauma of the hip (hip dyslocations, acetabular fractures) and in patients with FAI [1][2][3][4][5][6][7][10][11][12][13] , otherwise, it is the result of biological specific or nonspecific synovial hypertrophic pannus production [17][18][19][20] . Morphlogical bone changes in the area of the acetabulum and /or proximal femur in patients with FAI reduce physiological distance between these anatomical structures of the hip, lead to premature contact-impact of the femoral neck on the edge of the acetabulum, causing damage of the acetabular labrum and acetabular cartilage adjacent to it, but never lead to mechanical irritation of the articular capsule and its hypertrophic response.
We presented a patient with a clear clinical and radiographic picture of mixed form of FAI with normal biochemical, CT and NMR findings in which the subjective symptoms suddenly worsened after inta-articular application of corticosteroids in the hip joint.We found intraoperatively and verified histologically, a nonspecific reaction of the hypertrophic synovium, an unexplained etiology, that filled the hip joint, further decreasing the space between the edge of the acetabulum and the anterior and superor part of the femoral neck, with additional deterioration of the patient's subjective complaints, hip movements and irreversible damage of the acetabular labrum without the possibility to be reinserted but only partially resected.There were no reports in the literature to compare with our experience.We hypothesized, as a possible explanation, that the intraarticular administration of corticosteroids was the reason for the development of nonspecified hypertrophy of the hip synovium, but it needs furhter research.

Conclusion
We believe that young adults with pain in the groin and with normal biochemical, CT and NMR parameters should not be exposed to unnecessary and inappropriate treatment (skin traction, total hip replacement or intra-articular corticosteroid application), but to be appropriately operated on.