Hamstring Regeneration Following Harvest for Anterior Cruciate Ligament Reconstruction: A Review of the Current Literature

Abstract

The semitendinosus (ST) and gracillis (Gr) tendons are commonly used as a replacement graft during the anterior cruciate ligament (ACL) reconstruction. There are many advantages of using the hamstrings tendons, including the ease of harvesting, suitable morphology for use as a graft, lower donor site morbidity, early rehabilitation, and patient satisfaction.

In most cases, the ST tendon can regenerate after harvesting, showing similar morphology to the native tendon.

Although some researchers have demonstrated a loss of hamstring muscle strength in such patients, most investigators have found only slight differences between the operated and the controlateral side in the postoperative period. Recovery of the muscle strength after division of the ST and G tendons can be explained by a process of functional regeneration of the tendons or by compensatory hypertrophy of other knee flexors.

Morphological changes including atrophy and shortening of the ST have been confirmed in patients with ACL reconstruction using the ST tendon. MRI analysis has indicated a surprising potential for the harvested tendons to regenerate, in particular when only the ST, and not the G, has been used for autologous transplant. Both in vitro and in vivo studies have illustrated “intrinsic” and “extrinsic” healing potential of the injured or surgically reconstructed tendon, although some have shown a regenerative process of the full-length tendon.

The aim of this chapter was to present more information and morphologically document the regeneration ability of the semitendinosus after whole length and full thickness harvesting. The final question is if the quality of the regenerated tendons which resembled the normal ones would allow their use as a new graft.

Keywords

ACL reconstruction, hamstrings tendons, regeneration

Keywords

ACL reconstruction, hamstrings tendons, regeneration

Introduction

The semitendinosus (ST) and gracilis (Gr) tendons are commonly used as replacement grafts for anterior cruciate ligament (ACL) reconstruction, with advantages including the ease of harvesting, suitable morphology for use as a graft, lower donor site morbidity, early rehabilitation, and patient satisfaction.

The aim of this chapter is to present more information and morphologically document the regeneration ability of the ST after whole-length and full-thickness harvesting. The final question is if the quality of the regenerated tendons which resembled the normal ones would allow their use as a new graft.

Review

There are many advantages to using the hamstring tendons for ACL reconstruction, including ease of harvesting, suitable morphology, and lower donor site morbidity. It has not yet been shown, however, whether the overall donor site morbidity is less with hamstring grafts than bone–patellar tendon–bone grafts.

In most cases, the hamstring tendons can regenerate with a morphology similar to the native tendon after being harvested for use as an ACL graft. Cross et al. examined four patients randomly selected from a group of 225 patients 6 months postoperatively and found regeneration of the harvested ST and Gr tendons. Magnetic resonance imaging (MRI) provides clear details on the anatomy of the regenerated tendons from the muscle belly to the medial aspect of the gastrocnemius muscle so the postulated mechanism for regeneration occurs from the distal cut and the muscle belly, following the fascial planes to the popliteal fossa. Simonian et al. examined nine selected cases with MRI 3 years after harvesting both the ST and the Gr tendons and found newly formed tendons inserting below the level of the joint line in six of these cases. MRI was also done in an attempt to evaluate the cross-sectional areas of the biceps femoris, semimembranosus, and sartorius muscles, and documented no significant difference between operated and unoperated sides. Eriksson et al. evaluated 11 patients with MRI 6–12 months postharvest of the ST but not Gr tendon. Eight of these patients presented with newly formed ST tendons, and the insertion was reported to be as conjoined tendon together with the Gr in nearly anatomical position at the pes anserinus. In the three remaining patients, fusion of the newly formed ST tendon to the semimembranosus tendon was seen proximal to the joint line. Papandrea et al. studied the process of ST tendon regeneration by using ultrasound examination in 40 patients observed for 2 years after operation, and documented, in the early postoperative period, that regenerated tissue was significantly greater in the cross-sectional area than the normal ST tendon. As time progressed, a gradual reduction in thickness and a gradual return to a normal sonographic appearance was observed, and by 18 months postoperatively the regenerated tissue appeared very similar to the normal tendon. The recovery of hamstring muscle function and strength, after ACL reconstruction with the ST and Gr tendons, has been investigated by several authors. Although some researchers have demonstrated a loss of hamstring muscle strength in such patients, the majority of investigators have found only nonsignificant differences between the operated and nonoperated side in the postoperative period. Recovery of muscle strength after division of the ST and Gr tendons can be explained by a process of functional regeneration of the tendons or by a compensatory hypertrophy of other, undisturbed knee flexors. Understanding all these issues has practical implications for patient selection, recovery, tendon reharvest, and preferred graft source.

In most present studies, MRI has been used for examining the morphology of regenerated tendons. The reports of these studies analyzed the insertion of the neotendon, the morphology of the muscle tendon complex, and the time course of regeneration. The intact Gr may help the regenerating structure track to the pes anserinus and facilitate anatomic regeneration. Rispoli et al. documented the time course of tendon regeneration. In those patients who were 2 weeks from surgery, the harvest site defect appeared to be filled with fluid or edema. By 6 weeks, a solid structure with the morphology of normal tendon was present to the level of the patella. Over time this structure appeared to extend in a proximal to distal direction, and by 7–12 months it nearly reached the pes anserinus. Rispoli hypothesized that tendons first regenerate proximally in a more vascularized area, which then proceeds distally along fascial planes. Results from recently performed sonography as well as a biopsy specimen study showed that regeneration and maturation can be followed through time and that collagen fibers organization and structure is extremely important for those processes ( Fig. 30.1 ).

Open surgical investigation and biopsy with immunohistochemical analysis are the gold standard approach. In this manner, Eriksson et al. examined six patients who underwent tendon harvest 7–28 months previously. In five of six patients, a distinct solid structure had filled the harvest defect. Macroscopically, the structures had the smooth appearance of normal tendon; however, there were some rougher focal areas consistent with scarring. This provides indisputable evidence that some form of tendon regeneration occurs. Ferretti et al. performed a similar study with three patients who were 6, 24, and 27 months after tendon harvest. They reported that the regenerated tendon terminated as multiple adhesions on the fascia of the gastrocnemius, proximal and medial to the pes anserinus. At the histologic level, the neotendon is initially a fibrous structure, but over time it acquires many characteristics of a true tendon. At 6 months, the structure is predominantly fibrous, with only a few bundles of collagen fibers and capillaries, and fibroblastic proliferation is prominent. By 2 years most neotendons appear very similar to preharvest tendons. There are longitudinally oriented collagen fibers that appear to be of appropriate orientation and dimensions. However, there are also small focal areas of scar tissue with irregular collagen orientation, increased capillaries, and fibroblastic proliferation. The process of medial hamstring tendon regeneration proceeds through several stages characterized by edema fluid/hematoma, fibrous scar tissue, and finally, neotendon. This process takes approximately 18 months to reach completion and yields a neotendon that is similar to normal tendons in structure and composition, but it still retains some regions that resemble scar tissue. The neotendon restores a functioning muscle tendon complex that is able to generate tension ( Figs. 30.2 and 30.3 ).