Ali Bajwa, William McClatchie and Richard Villar outline how hip arthroscopy has become a viable option for the treatment of ligamentum teres injuries.
Interest in the role of the ligamentum teres (LT) of the hip has gathered pace recently. This short, intra-articular ligament’s anatomy has long since been well described ; however, the exact role of the LT in hip function has been less clear. The continuing expansion of hip arthroscopy has allowed a wide audience to evaluate the ligament closely and more accurately. The understanding of its role in hip function is evolving, and with it the consequences of its pathology and its ability to cause pain. Arthroscopic debridement and, more recently, arthroscopic LT reconstruction are becoming viable options for treatment of LT injuries.
The broad base of the LT originates from the transverse acetabular ligament, with two fascicles each arising from the periosteum of the ischium and pubic bones . The ligament is made up of collagen types I, III and V, and is arranged in three bundles that transform from a relatively flattened shape at the acetabular origin to an ovoid shape as it inserts into the fovea capitis. The blood supply is derived from the anterior branch of the posterior division of the obturator artery [2,3].
The intrinsic strength of the ligament has been compared with that of the anterior cruciate ligament (ACL). Porcine models have shown a load to failure of 882±168N compared with 633–814N for the ACL . When the ligament failed in this study it was seen to do so in a stepwise manner, suggesting a progressive peel-off from the acetabular surface.
The ligament has afferent sensory free nerve endings . This was seen in all samples taken from human LT, and in greater concentrations than seen previously in the ACL. The fibres provide somatosensory feedback that may have a role in preventing excessive and damaging motion of the joint. Nociceptive fibres have also been identified, with the greatest concentration at the middle portion of the ligament . Alongside the nociceptive fibres was an even greater concentration of unspecific nerve fibres, which may contribute to proprioception.
Previously considered a vestigial organ, much of the current work on studying the ligament’s function examines its ability to resist movement of the hip joint. It is put under most tension when the hip is flexed, adducted and externally rotated [7,8]. The LT is also put under significant stress when the hip is in flexion and external rotation, in other words the squatting position . The ligament moves about the joint depending on the position of the femoral head. It has been proposed that it plays a role in the circulation of synovial fluid around the joint . One cadaver study noted that the ligament positioned itself to resist translation of the femoral head. In abduction, the ligament lies inferiorly to prevent subluxation, while in external rotation the ligament sits anteriorly and prevents anterior translation .
Given the intrinsic strength of the ligament and its ability to resist extremes of movement it seems likely that it has a stabilising function. This is even more relevant when capsular stability is compromised, since capsule is a major contributor to the stability of the hip joint . However, the ligament has routinely been sacrificed previously, particularly for dislocation of the femoral head . It has yet to be proven if the absence of the LT increases the risk of dislocation. Despite this, it has been considered that LT and ACL of the knee show molecular analogy suggesting common functional properties and expression of similar biochemical mediators that confer identity to ligaments . Porcine studies have also shown that the LT and ACL share a similar fibroblast profile, which may explain the poor healing of both ligaments .
Insufficiency of the ligament may lead to microinstability, and an abnormal loading pattern within the joint. The concept of microinstability describes the failure to keep the femoral head centred within the joint, with the consequences of pain or mechanical symptoms . The mechanism is unclear, although both the loss of physical restraint and a loss of proprioception may contribute. Microinstability of the hip is analogous to the ACL insufficiency, in that the loss of normal kinematics may lead to accelerated chondral damage. This may be further exacerbated in exercise, as a high incidence of LT injuries has been seen alongside chondral and labral damage in elite runners .
Wear patterns of the hip have been studied arthroscopically in the presence and absence of LT tears . A difference was observed in the degree of chondral damage, but there was also a significant difference in the pattern of wear seen between the two groups. Both had signs of chondral damage at the anterior superior part of the acetabulum and anterolateral-to-lateral parts of the femoral head. This is commonly observed in femoroacetabular impingement. However, hips with damage to the ligament also had significant signs of chondral damage around the cotyloid fossa and to the apex of the femoral head, suggesting an altered loading pattern when the LT is damaged.
Incidence of tears
The incidence of LT injuries varies widely in the literature: earlier estimates were 4–15% . In a large series of 2628 procedures, one author found tears in 9% of cases . However, a more recent study of 558 hips identified an injury in 51% of cases . All of these studies are based on intraoperative findings. The sharp increase in reported injuries may be due to increased awareness of the significance of the LT, and a more thorough assessment of its morphological appearance intraoperatively.
Tears of the LT were originally classified by Gray and Villar .
- Type 1 injuries are complete tears and are often the result of disruption to the joint, usually from trauma or iatrogenic (Figure 1). Acute full-thickness tears are usually the result of violent trauma and typically are accompanied by significant damage to the bony architecture, cartilage and labrum.
- Type 2 is a partial rupture and tends to have a more chronic history (Figure 2).
- Type 3 are degenerative and are associated with osteoarthritis. In the original series, 60% of those with a Type 3 tear had a history of significant joint pathology, such as Perthes disease or slipped capital femoral epiphysis.
Of these, a partial tear is most commonly seen. In a series of 284 patients, Botser and colleagues found 21 patients had a complete rupture, 238 had a partial tear and 21 patients had a degenerative tear . As a result, the authors proposed a new classification that subdivided partial tears into less than 50%, and greater than 50%.
Risk factors for injury
Violent injuries causing hip dislocation and complete rupture are not common. Byrd and colleagues looked specifically at traumatic ruptures and noted complete rupture in only 12 of 23 cases . In the general population, partial tears are the most common injury, although the exact mechanism is unclear. Young athletes have a higher prevalence, particularly where a wide range of motion of the hip is required, and this has been previously recognised in ballerinas. It appears that forced external rotation of the hip with or without flexion and abduction puts the LT under stress and hence is likely to increase the risk of injury. In addition, iatrogenic complete tear of LT occurs in cases treated with open hip dislocation [2,20].
The osseous morphology is also relevant. Domb and colleagues reported that a lower centre-edge angle and higher acetabular inclination angle are both associated with an increased risk of tears . In addition, acetabular retroversion, as demonstrated by a prominent ischial tuberosity and positive crossover sign on plain radiographs, is also associated with higher rates of tears. The incidence of a tear of any sort rises with age, even within young adults.
There are few clinical features that are specific. A detailed history is essential, including any sporting activities undertaken, as this is the third most common cause of hip pain in athletes . A history of forced external rotation of the hip with the hip in flexion and/or hyperabduction may be present. However, authors have noted LT injuries in athletes reporting an injury sustained in hip extension with external rotation. Patients may complain of deep anterior groin pain, and may also describe symptoms of instability . Mechanical symptoms (catching, popping, locking) may be present, particularly following traumatic avulsions .
Examination findings and clinical signs are challenging to distinguish in the presence of co-existing articular injuries. Initially a reduced range of motion was thought to be relevant , although an increased range of motion has also been reported . The search for a specific clinical sign has led to the development of the Ligamentum Teres test . This places the hip in 70° of flexion and 30° short of full abduction. The hip is then internally and externally rotated to the extremes of movement. The presence of pain gives a positive result, and reversal of the provocative rotating movement should then relieve the pain.
Pre-operative investigations are unreliable for diagnosing tears. MRI is commonly used to assess the hip joint, and a reporting protocol would typically remark on the appearance of the LT. Botser reviewed the pre-operative MRI reports of 558 hips following arthroscopy . The sensitivity for identifying a tear was 1.8%.
Another study, using 3T MRI, found improved results. Devitt and colleagues found the sensitivity in diagnosing any pathology of the LT to be 50%, with a specificity of 34% . The sensitivity for reporting partial tears was 91%. By testing patients pre-operatively, and confirming the diagnosis intraoperatively, the authors showed the test to have a sensitivity of 90% and a specificity of 85%.
Arthroscopy plays a key role in identifying LT pathology. It allows visualisation of the ligament, along with instrumentation, and dynamic testing intra-operatively. With the ligament under arthroscopic view the leg is internally and externally rotated to allow dynamic assessment . It is possible that previously tears were being under-reported. This has changed recently; that more tears are being reported is possibly due to heightened awareness of the problem, and the benefits of treatment . The increasing uptake of arthroscopy contributes to a wider identification and interest in injuries to LT. The explanation given for the latter was that there were no intact free nerve endings to be stretched, hence no response. A specific clinical test becomes especially valuable when other diagnostic methods are unreliable.
Role of arthroscopy
Indications for treating LT injuries include persistent pain, mechanical symptoms and/or instability. Treatment of partial injuries is done by debridement using radiofrequency probes, while complete tears may require arthroscopic LT reconstruction [8,27]. During debridement, synovitis and exposed damaged bundles are removed, while preserving the intact fibres. There is also an opportunity to undertake the shrinkage of the ligament remnant. The LT reconstruction may be carried out using autograft, allograft or a synthetic scaffold [26,27].
The results for arthroscopic debridement are encouraging. It has been recognised that LT injuries are not usually treated in isolation, therefore assigning any clinical improvement to a single component of the operation is challenging. One study identified a cohort of 29 patients with an isolated ligamentum tear . All were treated with debridement and there was a significant improvement in the Modified Harris Hip Score and Non Arthritic Hip Score following surgery. Within this group, five patients had a recurrent partial tear that was attributed to ongoing instability. A further study carried out debridement of the ligament and capsulorrhaphy simultaneously. There were no recurrent tears in this group at an average follow-up of 32 months . Therefore, the goals of treatment should consider the problem of instability and carry out additional procedures if necessary.
Byrd and colleagues looked at 23 patients with a clear history of traumatic rupture . All patients improved following arthroscopic debridement. There was no difference in outcome between those with an isolated tear compared with those with additional articular injuries, nor was there a difference between those who had suffered a violent injury and those with a simple twisting injury.
The management of complete ruptures has been described with autograft and allograft (Figure 3) as well as synthetic scaffolds [26,27]. The indication for surgery is usually instability reported by the patient. Reports of techniques and outcomes has been limited to the case reports and series [26,27], but within these small numbers the outcomes have been positive.
The morphology of the LT has long been established, but more recently its microscopic properties have been characterised [5,6,12,13]. It shares several characteristics with the ACL , and the discovery of free nerve endings suggests a role in proprioception. More is also known about the role of the ligament in limiting motion of the hip, and the positions in which it is under maximum stress [9,20].
There has been an expansion in reporting arthroscopic findings; this is in part due to an enhanced appreciation of injuries to the LT. It is recognised that imaging cannot be wholly relied on to diagnose injuries [16,18,24], while arthroscopic assessment allows direct visualisation and instrumentation, as well as carrying out dynamic assessment. Abnormal chondral wear patterns have been reported in the presence of LT injuries [14–16]. This may be a consequence of microinstability.
Reports of arthroscopic treatment are encouraging [17,19,25]. Debridement for partial tears improves functional scores and reduces pain. Complete ruptures can cause subjective instability, which can be successfully treated with reconstruction [26,27].
Our understanding of LT is evolving rapidly. Pre-operative diagnosis with MRI is improving , and clinical tests are being developed . The success of arthroscopic treatment, and the appreciation of microinstability underline the importance of timely identification and treatment of injuries .
Disclosures: None relevant to this publication
(picture courtesy of A. Bajwa).
Ali Bajwa, William McClatchie and Richard Villar are all based at the Villar Bajwa Practice, Spire Cambridge Lea Hospital, 30 New Road, Impington, Cambridge CB24 9EL.