Recent advances and future trends in knee arthroscopy

ACL repair

Anatomic ACL reconstruction has been able to give excellent results with a high rate of return to sports. However, there are lacunae in this reconstructive approach such as loss of proprioception, graft site morbidity, surgeon errors in tunnel placement, residual instability, and a prolonged process of graft revascularization and incorporation.^[1] Hence, despite initial failure in this approach, there has been a resurgence of interest in ACL repair. Healing of the torn ACL following repair, provides an exciting opportunity of restoring knee stability with tissue which retains not only its native anatomy but also neurovascular supply.

The indications for ACL repair are acute femoral avulsions (Sherman Types I and II tears) of <3 weeks duration, with good quality tissue to be approximated, in young patients with lower activity levels and pre-injury Tegner activity scores <5. Isolated studies have documented good results in athletes and high activity groups too. However, the biggest hurdle to wide acceptability of ACL repair is the lack of convincing clinical data to support its regular use in clinical practice. This may change with time. At present, there are four different techniques of ACL repair described. These include refixation with suture anchors, internal brace ligament stabilization, dynamic intra-ligamentary stabilization (DIS), and bridge enhanced ACL repair (BEAR).

Refixation with suture anchors

Refixation with two suture anchors in the femoral footprint with alternate interlocking Bunnell type stitches in the two bundles of ACL has been described with varying success. Failure rates ranging from 15% to 25% have been reported.^[2,3] Early results, especially in adolescent patients, have so far been encouraging.^[4]

Internal brace ligament stabilization

Satisfactory 2-year patient outcomes and failure rates as low as 4.8% have been reported with internal brace ligament stabilization.^[5] In this technique, the proximal ACL rupture is reattached to the lateral femoral condyle with a looped suture tied over a cortical button on the lateral femoral condyle. The same cortical button is also used to fix a non-absorbable braided suture passed through the femoral condyle, through the substance of the ACL and tibial footprint and fixed on the tibia with an anchor. The central non-absorbable suture tape gives mechanical protection to the healing ligament. The addition of the internal brace has been shown to reduce the failure rates from 13.8% (without internal brace) to 7.4% (with internal brace).^[6] This technique has also been reported in three children aged 5–7 years, where the internal brace was removed at 3 months after healing. In all patients, the ACL healed on second look arthroscopy, and they returned to routine activities with results sustained at 2 years.^[7] DIS This technique builds on the internal brace technique with the belief that traditional ACL repair fails due to cyclical loading of the repair. A polyethylene wire is fixed on the tibial side with a spring screw mechanism which holds the tibia in posterior translation during all degrees of movements of the knee. Thus, the repair is protected leading to enhanced healing. A systematic review of 15 studies with Levels 1–5 evidence suggests that ACL repair using this technique is a safe and effective procedure in a select group of patients. The failure rates vary from 4% to 13.6%, and the revision rates varied from 2.1% to 15% at 1 year, and 7.9–11% at 2 years. The study noted that the long-term failure rates are comparable to ACL reconstruction in properly selected patients.^[8]

BEAR

The BEAR technique utilizes a bovine origin extracellular matrix scaffold augmentation in addition to the ACL repair to enhance healing of the torn ACL. The drawback is this technique requires a 5 cm arthrotomy. Only one human study has been done and reported good to excellent results at 2 years.^[9]

Individualized ACL reconstruction

Although ACL repair shows some promise, the gold standard for ACL tears remains reconstructive surgery. What is increasingly recognized is that “one size does not fit all.” Anatomical variations in size and shape of the bones and ligaments, along with varied patient factors and functional demands may not allow the same standardized reconstruction in every knee. Hence, the concept of individualized ACL reconstruction has been proposed.^[10] The principles of this include: Appreciate the native anatomy, individualize surgery according to patient needs, place the graft in the center of footprint, attempt to fill in about 80% of the footprint surface, and tension the grafts individually if performing a double-bundle construct. Routine notchplasty is discouraged as it may lead to bone overgrowth and impingement at a later date. Although the ideal graft, technique, fixation, and need for augmentation will continue to be debated, the following information, determined based on recent meta-analyses, may be applied to individualize ACL reconstruction.

Single-bundle versus double-bundle reconstruction

A Cochrane database review found no difference in pain, complications, graft failure, and subjective knee scores at short- and long-term follow-up in patients with single- and double-bundle ACL reconstruction. However, patients with double-bundle reconstruction were better in terms of IKDC knee examination, knee stability with KT-1000, rotational knee stability, with better prevention of meniscus injury.^[11] A recent meta-analysis of randomized controlled trials with at least 5 year follow-up found no difference in the objective stability, subjective IKDC, Lysholm and Tegner scores, graft rupture, and osteoarthritis changes between a double- and single-bundle reconstruction. However, the meta-analysis included <300 patients from 5 studies. Hence, over the past 3 years, the enthusiasm for double-bundle reconstruction has waned.^[12]

Graft choices in ACL reconstruction

No clear scientific data exist that clarifies whether one graft is superior to the other, however, there seems to be a slow shift in choice of graft, as hamstring tendons are now used at least as often as patellar tendon as an ACL graft because there appears to be less morbidity with hamstring graft use.

In a meta-analysis on graft choices for ACL reconstruction which compared objective stability scores, subjective IKDC and Lysholm scores, graft failure rates and pain scores, patients with a quadriceps tendon graft had lesser graft harvest site pain than BPTB graft, and better Lysholm score than hamstring autograft, while all the other variables were similar.^[13] The rupture rates with BPTB grafts are lesser than hamstring autografts although the difference is miniscule. The objective stability and clinical outcomes do not differ.^[14] Soft-tissue allografts are inferior to autografts for primary ACL reconstruction in terms of the lower IKDC score, and objective stability scores.^[15] For revision knee reconstruction autografts and non-irradiated allografts have been found to have similar objective and subjective outcome scores. Irradiation of allografts makes them an inferior choice of graft for primary and revision cases.^[16]

Graft comparative rate of infection

In terms of post-operative infection after ACL reconstruction, using a patellar tendon autograft has a 77% lesser incidence than hamstring autograft, and 66% lower incidence than all types of other grafts. At the same time, autografts and allografts did not differ in the incidence of infections.^[17]

Antero-medial portal (AM) versus trans-tibial (TT) technique

A meta-analysis of randomized trials found that patients with AM technique had better subjective scores (IKDC, and Lysholm) and objective stability (Lachman’s, Pivot shift, and side to side difference) as compared to TT technique.^[18]

Fixation devices

A Cochrane database review found very low quality evidence that bioabsorbable screws are associated with more treatment failures, including intra-operative breakage, although the subjective and objective outcome scores are similar.^[19] A meta-analysis of level one studies did not find any difference between a cortical button, cross pin, and interference screw for fixation on the femoral side for hamstring autografts.^[20] For quadrupled hamstring grafts aperture fixation led to >3 mm but <5 mm side to side difference on KT-1000 measurements and a significant increase in graft ruptures as compared to suspensory fixation. Other stability measures and patient outcome scores were similar.^[21]

Return to sports

The rate of return to sports after a primary ACL reconstruction is 83%, with a 5.2% re-rupture rate.^[22] The reported rates of return to sports at the same level after revision ACL reconstruction is only 43%, even if 73% patients had a good to excellent subjective and objective result.^[23] In children and adolescents, the rate of return to pre-injury level of sport was 78.6% and that to competitive level of sport was 81.0%. Overall, 13% patients had graft re- ruptures, and in 14% contralateral ACL injuries were reported.^[24]

Remnant sparing ACL reconstruction

With the recent trend of preservation and repair in knee arthroscopy, surgeons are increasingly sparing viable ACL remnants during reconstruction [Figure 1]. Evidence suggests that preservation of the ACL remnant is beneficial in terms of vascularity and proprioception, which may improve recovery of joint position sense, and enhances revascularization and integration of the graft.^[25-27] Remnant sparing may be in the form of tibial remnant re-tensioning, specific bundle reconstruction for partial ACL tears, and remnant sparing where the graft is passed through the tibial tunnel and within the remnant. The most recent meta-analysis of Levels 1 and 2 studies determined that remnant sparing ACL reconstruction is not vastly superior to traditional ACL reconstruction, and there is no difference in the healing of grafts, or the overall complication rates. However, remnant sparing results in better objective stability in terms of KT 1000/2000 measurements, and better Lysholm scores.^[28]

Close

Figure 1:

Remnant sparing anterior cruciate ligament (ACL) reconstruction. (a) MRI reveals a recent ACL femoral avulsion of Sherman Type II (b) arthroscopic technique involves (i) identifying the ACL femoral avulsion and creating tunnels at the anatomical insertion sites, (ii) inserting a curved suture anchor anterior to the ACL femoral tunnel within the footprint of the ACL, (iii) passing one limb of the suture in mattress configuration through the ACL remnant, (iv) ACL graft passage while retracting the ACL stump, (v) a knot is now applied to the sutures so that the remnant envelopes the ACL graft and is fixed to the femoral insertion footprint.

Export to PPT

Biologics in knee ligament surgery

Platelet-rich plasma (PRP), platelet-rich growth factor, and stem cells have all been used along with ACL reconstruction and repair in an attempt to improve graft healing. Despite encouraging results in pre-clinical studies, a systematic review and level one study concluded that the role of these is still controversial. There does not seem to be any improved graft maturation over time, and no benefits in clinical outcome, bone integration, and prevention of bone tunnel enlargement.^[29] Autologous bone marrow aspirate concentrate (BMAC) has shown promise in ACL femoral avulsions without retraction. However, further level one studies would be needed to prove the utility of bone marrow procedures.^[30]

ACL reconstruction in skeletally immature patients

Several Levels 3 and 4 studies, and a meta-analysis of the studies,^[31] have proven that early surgery is preferable in skeletally immature patients as compared to non-operative treatment. Delaying treatment for more than 12 weeks results in four-fold rise in medial meniscus injuries, and increased odds ratio of lateral condyle and medial condyle chondral injuries of 5.6 and 11.3, respectively.^[32] There are three techniques of ACL reconstruction in skeletally immature patients: Transphyseal, physeal-sparing, and hybrid techniques. It is recommended that whenever the physis needs to be violated the tunnel should be as perpendicular and central in the physis as possible. The technique to be chosen has been defined according to bone age and physeal growth potential.^[33]

Role of bony morphology

An increased tibial slope, especially lateral tibial slope, has been shown to increase shear forces and stress across the ACL in biomechanical studies.^[34] In a meta-analysis; an increased tibial slope has been associated with increased risk of ACL injury.^[35] Decreasing posterior tibial slope has been shown to be vital in preventing failure in patients with increased tibial slope undergoing revision ACL reconstruction. It is believed that a posterior tibial slope of 13° or more needs to be corrected in the revision situation to around 5°.^[36] The role of bony correction in primary ACL reconstruction is controversial. Other bone morphological features which are postulated to predispose to increased risk of ACL injury and failure of ACL reconstruction are shallow medial tibial plateau (deeper medial tibial plateau constrains the femur better), a shorter medial tibial plateau, lower volume of medial tibial spine, a dome shaped inter-condylar notch (pyramidal notch maintains better stability), and spherical medial femoral condyle (ovoid shape is more stable).^[37] Further studies using 3D imaging and statistical shape modeling may help in the future to better delineate the role of bony morphological variations in knee stability. This may also help to predict athletes at high risk for ligament tears, and perhaps formulate better guidelines for bony correction in primary ACL reconstruction.

The effect of hormones and ACL injury prevention programs

In females, the relative risk of ACL tear is highest during the ovulatory phase, followed by the follicular phase, and least in the luteal phase. Oral contraceptive pills provided 20% reduction in risk of injury.^[38] Women had higher rate of second ACL injuries (6.84%) than men (5.67%). Overall women suffer more re-ruptures and contra-lateral ACL tears as compared to men.^[39]

A meta-analysis found that ACL prevention programs did decrease the incidence of ACL injuries in all athletes by 50%, especially in female athletes.^[40] Neuromuscular and proprioceptive training also decreases the rate of injuries, but no specific group of exercises is superior.^[41]

Meniscal allografts

These have consistently given good results in appropriately selected patients in the long term.^[55] However, there are concerns which include graft size mismatch, questionable long-term chondroprotection, low rate of return to sports, progressive joint degeneration, graft sterility and incompatibility, limited availability in many countries, and low rates of remodeling and stability.

Meniscal scaffolds

It may be useful when there is segmental loss of meniscus <5 cm with an intact peripheral rim. A scaffold theoretically allows for native cells and tissue to grow in, while it biodegrades over a period of time. There are two different types of scaffolds: Collagen meniscus implant (CMI) made from bovine collagen matrix, and polycaprolactone- polyurethane scaffold (Actifit). Both have shown mixed results in patients with up to 10 year follow-up for CMI device,^[56] and up to 6 years follow-up in case of Actifit device.^[57] In a systematic review, both the devices have been found to be similar in terms of patient outcomes.^[58] A 12.6% rate of complications has been reported which includes pain, effusion, infections, debridement for non-integrated scaffolds, re-tears, and scar tissue removal. A failure rate of 9.9% at 40 months for Actifit, and 6.7% at 44 months, for CMI device have been reported.^[58] A scaffold which can produce high quality in vivo results in everyone has not yet been found.

Tissue engineering and regenerative medicine for scaffolds

Research is progressing in this field whereby these scaffolds will be 3D printed and impregnated with either autologous cells from the meniscus, or stem cells, and growth factors, which can then be cultivated in a bioreactor to get a patient-specific tissue engineered meniscal implant which is fully biocompatible.^[59]

Gene therapy for meniscus regeneration

Encouraging results have been reported by gene therapy, whereby favorable genes can be introduced into target meniscal cells to encourage regeneration.^[60]