Controversies in the Management of Anterior Cruciate Ligament Injuries in Skeletally Immature Patients

A Literature Review of Current Treatment Options

Amr Selim, MBChB (Hons), MRCS, MSc Orthopaedics; Humza Tariq Osmani, BSc (Hons), MBBS (Dist), MRCS; Wasim Khan, MBChB, MRCS, Dip Clin Ed, MSc, PhD, FRCS(Tr&Orth); Ioannis Pengas, MBChB, MRCS, FRCS (T&O), MPhil (MedLaw & Ethics), MD

Disclosures

Curr Orthop Pract. 2022;33(2):197-203. 

In This Article

Results

Nonoperative Management

Kocher et al.[10] recommended immobilizing the knee and restricting weightbearing for treating partial ACL ruptures in children with physical therapy that focused on strengthening the hamstring and the using a brace during sports. Despite this "restrictive" regimen, 31% of the nonoperated patients required surgical intervention because of instability or recurrent injury.[10]

A systematic review identified only one study in which no difference in outcomes were found between operative and nonoperative management for complete ACL tears.[11] The authors attributed this to the complete abstention from sports and the daily use of an ACL knee brace in the nonoperative group.

Compliance with nonoperative management requiring such a level of restriction is often challenging in this physically active demographic.[12] Numerous reports[4,8,13,14] have outlined the increased association of meniscal tears, which potentially may be irreparable, or cartilage damage because of delaying surgery after ACL injury in the skeletally immature patient. In data collected over 18 yr, Weitz et al.[4] reported a prevalence of instability up to 75% in those treated nonoperatively compared with 13.6% in those who had an ACL reconstruction. This for some is more concerning than the potential risk of growth arrest and graft failure.[13]

Surgical Intervention

The optimal management of ACL ruptures in children remains controversial. Although surgical treatment is now widely used to restore stability and prevent the aforementioned sequelae, the challenge associated with physeal damage and early failure is concerning.[15] Particular controversies include the timing of surgery, type of graft, and location of tunnels.[12] Stakes are particularly high in very young children with significant growth remaining, or adolescents with little growth potential.[12,16] However, where deemed appropriate, surgical options include ACL reconstruction and ACL repair.

ACL Reconstruction. Standard ACL reconstruction involves drilling and passing the graft across the open physis. This potentially can cause physeal damage, especially when the tunnel is placed obliquely, which is biomechanically favorable. By doing so, the cross-sectional area of the tunnel is increased within the physis, which in turn may result in greater physeal damage. This problem is exacerbated on the femoral side where the distal physis has an undulating orientation.[12]

Timing of surgical intervention is also critical; early ACL reconstruction in children within 6 wk demonstrated improved results and three times fewer medial meniscal tears, whereas delayed operative intervention has been attributed to higher rates of meniscectomy and lower subjective outcome scores.[14]

Of concern, ACL reconstruction in patients with open physis has higher rerupture rates when compared with the adult population. Astur et al.[15] reported that in a population of over 1300 ACL reconstructions, those below 16 yr of age had a revision rate of 24.6%, compared with 17.5% in those between 16 and 18 yr of age and 9.2% in those over 18 yr old. Although there are many factors that lead to graft failure, this highlights the increased risk of failure that exists in the pediatric population. Although the total number of subjects included in their study seemed impressive, the actual numbers in the two subgroups under the age of 18 were low and could lead to Type 1 error.

However, within the literature, other papers concur that skeletal immaturity and ages below 18 to 20 yr do have higher rerupture rates. Bourke et al.[17] noted a three-fold increase in graft rupture in children compared with adults using the same operative technique and postoperative protocol. The Danish registry also supports this finding, reporting a revision rate after primary ACL reconstruction over three-fold higher in patients under 20 yr of age when compared with adults.[18]

Graft Choices. Smaller graft diameter has been identified as a potential cause of failure,[19] and mature hamstring allograft has been reported by Pinczewski et al.[20] among others to be a solution.[15] Attempts to solve the "problem" by the use of allograft tissue from an unrelated donor demonstrated a higher failure rate in primary pediatric ACL reconstruction.[21] Allograft donated by parents provides biologically active tissue that is greater in diameter and is associated with better postoperative outcomes and failure rates; however, the associated donor-site morbidity and potential risks to the uninjured parent could be undesirable.[22]

Techniques

Transphyseal ACL Reconstruction. The greatest challenge in these patients is avoiding iatrogenic physeal damage, which could cause growth disturbance, limb-length discrepancy, or angular deformity.[10] It is known that the distal femoral physis contributes 9 mm to 10 mm per annum (40% of lower-extremity growth), and the proximal tibial physis contributes 5 mm to 6 mm per annum.[23] Growth charts can be used to determine a patient's final stature and calculate potential leg-length discrepancies. However, expected growth is affected by various factors including the timing of puberty and bone age, which itself may be delayed because of multiple factors including endocrine and nutritional factors. The two main methods for assessing bone age are Tanner-Whitehouse (T-W) and Greulich-Pyle.[24] Both methods calculate using hand radiographs. Time of puberty is the other important factor because it provides an estimate of the remaining growth. Some predictors estimate that 3 yr of growth remains after the onset of puberty, which, on average, occurs at age 11 yr for girls and 13 yr for boys. Others estimate it as 2.5 yr, with an initial rapid growth phase during the first year after onset of puberty and a subsequent slowing down phase of 1.5 yr.[25]

Physeal injuries can lead to the formation of physeal bridges, which in turn result in growth arrest and skeletal deformities. However, excision of these is not recommended unless there is 2 cm or 2 yr of remaining growth,[26] because there is less growth potential to correct the deformity or arrest.[25] The distal femoral physis is particularly vulnerable to growth arrest and deformities because of its irregular contour and high proliferative potential.[26] The use of anatomical landmarks and fluoroscopy are recommended to achieve anatomic reconstruction and avoid physeal damage.[27,28] Transphyseal tibial drilling is of lesser concern because this tunnel is situated more centrally within the physis, and its shape can be made more circular by increasing the tibial aimer angle. In addition, it's creation usually requires removal of less than 3% of the physeal volume,[29] which doesn't significantly devitalize the physis. It has been shown that up to 7% of physeal volume can be safely removed, especially if soft-tissue graft material alone is placed across the physis.[30]

Most angular deformities and growth disturbances have been associated with bone plugs or fixation devices deployed across or against the physis.[31] Avoiding fixation devices (nonabsorbable) from crossing the physis,[30] incomplete filling of the tunnel with graft,[28] excessive graft tensioning,[32,33] as well as utilizing a bone patella-tendon-bone graft (because of the potential formation of an osseous bridge) has been recommended.[34]

Despite these risks, transphyseal ACL reconstruction is performed frequently in skeletally immature patients with good outcomes, minimal growth disturbance, and a high rate of return to previous activity levels.[17]

Physeal-Sparing ACL Reconstruction. A few physeal-sparing reconstruction techniques (Figure 3) have been proposed to avoid impaired growth. The extraarticular Macintosh technique[35] and its modifications have shown good results in several studies without growth deformities.[11] More contemporary intraarticular procedures, using single or both physeal-sparing[36,37] techniques, have been described with both methods yielding good results.[11] Risks of the physeal-sparing technique include it being technically demanding because of the size of the epiphysis, and the angle required to keep the graft away from the physis.[38] The acute angle can furthermore lead to increased stress across the graft.[38] Furthermore, a meta-analysis of 55 studies (935 patients) of ACL surgery in skeletally immature patients revealed that the physeal-sparing, transosseous group had a 5.8% risk of growth disturbance or axis deviation compared with 1.9% with the transphyseal techniques. They also reported the rerupture rate to be 1.4% in the physeal sparing technique and 4.2% in the transphyseal group.[39] More recent rates of growth disturbance after reconstruction have been reported as high as 2.6%.[4] Physeal damage can be caused by the deleterious effects of drilling parallel to the physis, which results in thermal injury, or from a pressure effect of the implant on the growth plate.[11] Overall, it does appear that the rate of growth disturbance may be under reported, as many surgeons do not routinely assess for it during the follow-up.[39]

Figure 3.

Methods of anterior cruciate ligament (ACL) reconstruction in pediatrics.

ACL Repair

Surgical repair of the ACL is proposed as an alternative to reconstruction. The reasoning behind this is the perceived avoidance of a number of potential problems, including the morbidity of parental allograft or autograft harvest, inadequacies associated with autologous grafts, and the documented loss of proprioception.[40,41] It requires an ACL remnant that is repairable, ideally with a proximal femoral peel-off type of injury, as described by Sherman et al.[42] The attraction of this technique, with its less extensively published outcomes,[43,44] is the limit of bone involvement being less than all other "traditional" methods, including the all-inside socket method. This may be important in the demographic of patients who are presenting before physeal closure. A second procedure could be necessary for the removal of the protective tape construct that may be used, such as, FiberTape (Arthex Naples, Florida). This procedure is not always utilized, as described by DeFelice et al.[45] Any failure of this technique does not preclude future ACL reconstruction by any other method.

ACL repairs were not viewed favorably after previous open techniques.[46] Observed midterm outcomes were unsatisfactory with persistence of pain, swelling, and instability (71%, 66%, and 94%, respectively) and this was mirrored in other studies based on the same open technique.[47] Long-term clinical outcome studies also reported poor outcomes with high rates of additional surgery (64%) and ACL reconstruction as a result of ongoing instability of up to 24%.[48] Explanations for these poor initial results include the initial use of arthrotomies, which diagnosed "isolated" ACL injuries without an appreciation of concomitant meniscal injuries. Newer arthroscopic techniques are more able to diagnose other injuries, thus enabling the surgeon to achieve better stability though addressing multiple pathologies in one sitting.[47] However, Gagliardi et al.[49] reported a 48% rerupture rate in the first 3 yr in pediatric patients who underwent suture repair reinforced with tape, compared with 4.7% in those who had a patella-tendon-bone ACL reconstruction.[49] Subsequent case series[42,43,50] demonstrated good outcomes in those who had repairs for proximal peel-off injuries (Sherman I and II), thus emphasizing the importance of choosing the right type of injury and patient for ACL repairs.

A systematic review of level I studies[51] comparing ACL repair versus reconstruction, demonstrated a cumulative revision rate of 15.6% in hamstring ACL reconstructions, which is similar to 15% reported by Actnicht et al.[52] This latter study also demonstrated similar outcomes at the 2-year postoperative stage between suture anchor repair of acute proximal ACL avulsion tears and single-bundle ACL reconstruction. Other studies have also reported encouraging results.[53] One such study looked at 5 to 6-year outcomes in pediatric or adolescent patients and observed that approximately 33% of patients reported excellent Lysholm scores, and 41% of the patients had final instrumented laxity measurements of less than 3 mm.[54] A recent randomized control trial from 2019 conducted by Hoogselag et al.[55] demonstrated dynamic augmented suture repair was not inferior to ACL reconstruction based on patient self-reported outcomes at 2 yr after surgery. Reconstruction in this trial utilized the single-bundle hamstring tendon technique. At the 2 yr point, 8% of patients who had a repair had a rerupture, and 19% suffered that in the reconstruction group. However, 20% of patients in the repair group had related adverse events leading to repeat surgery, which also must be considered when considering the morbidity associated with the procedure.

Important Factors for ACL Repairs. Timing from injury to operation seems to play a crucial role when it comes to ACL repair. A group of Yorkshire pigs underwent enhanced bilateral primary ACL repair in a staged fashion demonstrating that immediate repair had more favorable outcomes when compared with those with 2- and 6-week delays.[56] Another pig-based experimental study of primary repair demonstrated less posttraumatic osteoarthritis in the repair than the reconstruction group at 12 mo.[57] This may be explained by the fact that ACL repair potentially could maintain proprioception and restore native knee kinematics,[58] but it has published that ACL reconstruction perhaps does not do so.[59]

The production of a "healing response" was proposed by Sherman et al.[42] via the use of an arthroscopic awl by producing 6 to 10 holes in the cortical bone of the femoral ACL footprint. This surgery was performed early (mean of 22 days after injury) in skeletally immature patients, and all had proximal one-third ACL disruptions (Sherman 1 to 2). Out of the 13 patients treated in this fashion, three failed because of subsequent reinjury at 42 mo, but those that survived demonstrated a side-to-side improvement, and all patients considered their knee function to be normal at 69 mo after surgery.[42]

Age may be another important factor in the healing response.[60] Murray et al.[60] took 21 Yucatan pigs of varying skeletal maturity (juvenile, adolescent, and adult) and transected both ACLs in each pig. One side was left untreated, and the contralateral side was repaired with sutures incorporating a collagen-platelet composite. Biomechanical properties of the repair and histologic analysis was performed. Results indicated that in both groups, the younger skeletally immature pigs had a more productive healing response than mature animals. In the adolescent group, the repaired ACLs had an 85% increase in load that was withstood compared with the nonoperated side indicating a less productive inherent healing response as pigs became older.

The importance of a suitable biological environment is also highlighted by other studies in the form of a collagen matrix sponge or platelet-rich plasma (PRP) to stimulate healing.[61,62] These suggest that their relationship is mutually inclusive. That is, augmentation with either a collagen scaffold or PRP in isolation does not seem to improve the biomechanical or the histologic properties but combining both seems to affect healing positively.[62]

A more recent study by Murray et al.[63] in 20 patients (10 in each group) compared hamstring autograft ACL reconstruction versus a bridge-enhanced anterior cruciate ligament repair (BEAR), which involves repairing the ligament with sutures combined with a bioactive scaffold. The study found no differences in pain, or graft integrity, with hamstring strength at 3 mo better in the "BEAR" group. These initial results are encouraging and would benefit from a larger study.[63]

Furthermore, a stable environment offered by an internal augmentation strut composed of 3 mm polyethylene terephthalate traversing both the femoral and tibial tunnels demonstrated improved histological evidence of healing when compared with a nonaugmented construct in a study based on mountain sheep with serial sampling up to 52 wk postoperatively.[64] In their follow-up study, they demonstrated that suture repair plus strut showed less laxity and greater tensile strength than suture repair alone.[65]

Limitations and Future Perspectives

The perceived advantages of repair instead of reconstruction are the decreased morbidity along with native tissue preservation perhaps leading to better proprioception and joint kinematics. This makes repair at any age, but mostly in the skeletally immature individual in whom rerupture rates are higher, an interesting proposition. Thus, although there are some encouraging outcomes from studies assessing ACL repairs, many studies continue to demonstrate variable clinical outcomes and inconsistent failure rates. This perhaps reflects the short follow-up results available and the heterogenous nature of repair techniques. Moreover, many of the studies that have reported ACL repair are animal based, and more investigation in the form of human randomized multicenter studies with medium- to long-term outcomes are desirable. One such initiative is the European Society of Sports Traumatology, Knee Surgery and Arthroscopy (ESSKA)-driven Paediatric Anterior Cruciate Ligament Monitoring Initiative (PAMI) initiative. It was established in 2013 aiming to enlarge the evidence base for optimal treatment of pediatric ACL injuries; this is further strengthened by large scale studies being conducted, although the need for more is clear.[66]

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