In a study with a long-term follow-up,⁷ kneeling pain was found to persist even at 7 years postoperatively and was more common and more severe in the patellar tendon group (54%) than the hamstring tendon group (20%). Similarly, the incidence of donor site symptoms in any form was more than doubled in the patellar tendon group compared with the hamstring tendon group, and the incidence of extension deficit increased over time in the patellar tendon group, probably secondary to development of osteoarthritic changes.⁷

But what causes anterior knee problems after patellar tendon harvest?

Harvesting trauma, patellar tendonitis, tendon changes during the repair process of the tendon gap, vascular damage of the retropatellar fat pad, and proprioceptive loss of the extension mechanism are all possible causes.¹⁴ Patellar tendon shortening is another important factor for development of anterior knee pain. It has been demonstrated with a magnetic resonance imaging (MRI) study¹⁵ that significant patellar tendon shortening (with a mean of 9.7%) occurs after harvesting BPTB graft compared with the contralateral nonoperated control knee 1 year after ACL reconstruction (Fig. 79-1).

Fig. 79-1 A, Measurement of the patellar tendon length in a sagittal magnetic resonance image (MRI) of a knee 16 months after anterior cruciate ligament (ACL) reconstruction with bone–patellar tendon–bone graft. B, Sagittal MRI of the contralateral healthy knee (3-mm difference, or 6.6%).

A possible explanation for this is the retropatellar fat pad fibrosis secondary to the surgical trauma, contraction of the scar that develops in the gap created after patellar tendon harvesting due to diminished elastic components, and the decreased strength of quadriceps contributing to patella baja, which stresses patellofemoral joint. Moreover, quadriceps inhibition/weakness causes delayed rehabilitation with subsequent extension deficit and abnormal patellofemoral joint forces.

In contrast, harvesting of hamstring tendons resulted in a nonsignificant shortening of the patellar tendon of 2.6% (Fig. 79-2). Using an Insall-Salvati ratio less than 0.74 as the MRI criterion for patella baja diagnosis,¹⁶ 12.5% of the patients in the BPTB group and 3% in the hamstring group were found to develop patella baja after surgery. This shortening was not of clinical importance, as it was not associated with anterior knee pain in the short-term follow-up. However, one other study with longer follow-up (average 7 years) has clearly shown that severity of patellofemoral joint arthritis and anterior knee symptoms correlate with the amount of patellar tendon shortening¹⁷ (Fig. 79-3).

Fig. 79-2 A, Measurement of the patellar tendon length in a sagittal magnetic resonance image (MRI) of a knee 14 months after anterior cruciate ligament (ACL) reconstruction with hamstring (HS) graft. B, Sagittal MRI of the contralateral healthy knee (1-mm difference, or 2.6%).

Fig. 79-3 A, Symptomatic patellofemoral arthritis in a young patient 4 years after anterior cruciate ligament (ACL) reconstruction with bone–patellar tendon–bone graft. B, Management with anteromedial tibial tubercle transfer (Fulkerson osteotomy).

Central patellar tendon harvesting has been found to cause a slight medial displacement of the patella,¹⁸ and this alteration in position causes high contact forces in the medial patellofemoral joint.¹⁴ A solution to this may be the use of the medial third of the patellar tendon, which does not influence the patellofemoral angle and causes an insignificant lateral patellar displacement.¹⁸

Anterior knee pain does occur after hamstring ACL reconstruction, despite the fact that the anterior structures of the knee remain intact. The reason for this is not clear, but it is known that the patellofemoral joint can be the source of pain after almost any surgery to the knee, even if the patellofemoral extension mechanism is not directly involved. The incidence of anterior knee pain after hamstring graft for ACL reconstruction in the literature is less than 23%.¹⁹^–²² Evaluation of the pain with diagrams has shown that it is more diffuse and is not related to the skin incision for tendon harvesting or tibial tunnel drilling.¹⁹ In contrast, anterior knee pain after patellar tendon harvesting is more well localized, and palpation reveals trigger points that are usually over the inferior pole of the patella or the tibial tuberosity or above the patellar tendon donor site.^14,²³

There are conflicting reports in the literature on whether grafting the patella and tibial tunnel bone defects after BPTB harvesting reduces ^23,²⁴ or does not reduce²⁵ the incidence of anterior knee symptoms. There is also a report that patella grafting increases the incidence of painful spurs at the inferior pole of the patella.²⁶ Similar arguments exist regarding whether suturing the patellar tendon gap facilitates tendon healing or is a cause of patellar tendon shortening.²⁷ Patellar fracture is another important issue unique in BPTB grafts, and its incidence varies from 0.2%²⁸ to 2.3%.²⁹

Patellar tendon rupture is another rare complication that may occur after patellar tendon harvest. Devascularization and an alteration in tendon healing and remodeling are possible causes of this complication.³⁰

Central Quadriceps Tendon

Use of quadriceps tendon autograft has been introduced to overcome disadvantages of patellar tendon and hamstring grafts. Literature is limited on the use of this graft, but initial experience has been promising with regard to anterior knee problems.

In a recent study, less than 10% of patients with quadriceps tendon graft suffered anterior knee pain in various activities, and only 6% complained of kneeling pain.³¹ Donor site irritation over the proximal patellar border was observed in several patients but did not last more than 6 months, and quadriceps strength 1 year postoperatively was comparable with that of other autografts in the literature.³¹ The risk of patellar fracture must be lower than that of patellar tendon graft because the bone in the proximal patellar pole is more dense.³² Injury of infrapatellar branches of the saphenous nerve is not a problem because the incision does not cross them.

Allografts

During the past 30 years, allografts have been used commonly to reconstruct the ACL as an alternative to reduce donor site morbidity. Allograft choices consist of patellar tendon, quadriceps, hamstrings, Achilles, and anterior and posterior tibialis tendons and fascia lata. The most commonly used at present is BPTB allograft. The improved sterilization techniques with cryopreservation, which does not interfere with the mechanical properties of the graft, contributed to a rise of allograft use during recent years.

Some studies comparing patellar tendon autograft versus allograft in ACL reconstruction failed to show any difference in the incidence of anterior knee pain between the two groups.^33,³⁴ Others found a significant reduction in anterior knee pain with allografts, such as 14% versus 46%³⁵ and 14.4% versus 55.8%.³⁶

In a study comparing patellar tendon autograft versus allograft with long-term follow-up (5 years), it was found that the autograft group experienced more pain during the first 3 postoperative months, which relates to the larger incision required and the resulting bony defect.³⁷ At 2 and 5 years there was no difference in the pain. Moreover, both in the short and long terms, there was no difference in the range of motion and quadriceps strength.

However, incision site complaints (tenderness, irritation, numbness) are less common in the allograft group when compared with the autologous BPTB group.³³

Anterior Knee Problems Related to the Procedure

The infrapatellar branch of the saphenous nerve has two main trunks, superior and inferior,³⁸ coursing laterally and slightly distally, respectively (Fig. 79-4). Incisions close to the tibial tubercle and over the patellar tendon may damage these branches with consequent anesthesia, dysesthesia, or painful neuroma formation.³⁹ A significant correlation exists between disturbed anterior knee sensitivity and subjective anterior knee pain as well as discomfort during knee walking.^40,⁴¹ Moreover, there is an association between injury of these sensory branches and development of reflex sympathetic dystrophy.³⁷ The importance of infrapatellar branches can be appreciated by reports of prepatellar neuralgia after direct blows to the anterior knee.^42,⁴³

Fig. 79-4 The infrapatellar branch of the saphenous nerve with the two main trunks, superior and inferior, coursing laterally and distally.

(Reprinted with permission from Kartus J, Ejerhed L, Sernert N, et al. Comparison of traditional and subcutaneous patellar tendon harvest. A prospective study of donor site-related problems after anterior cruciate ligament reconstruction using different graft harvesting techniques. Am J Sports Med 2000;28:328–335.)

Patients should be informed of these potential complications. The area of anesthesia is variable but always lateral to the incision. It is not only the incision for graft harvesting that puts in danger these sensory branches; the incision for the medial portal can damage them as well.^38,³⁹ Therefore some propose a horizontal rather than vertical incision for the portals to minimize the risk of nerve damage.³⁸ Another maneuver to avoid damage of these nerves is placing the anterior midline skin incision with the knee held in 90 degrees of flexion. In this way the inferior branch moves farther distally and the risk of inadvertent damage is lessened.³⁸

When harvesting patellar tendon autograft with a small midline incision, every effort should be made to identify and protect these sensory nerve branches. Alternative techniques have been described for subcutaneous patellar tendon harvesting using two horizontal incisions,⁴⁴ one horizontal incision at the midlevel of the patellar tendon,²³ and two vertical⁴¹ incisions. This way the infrapatellar branches are avoided, making these incisions less likely to become a source of pain.

Injury to these branches can occur not only during patellar tendon harvesting but with hamstring tendon as well. Anterior knee sensory changes were found to be as high as 50% (at a minimum of 24 months postoperatively) following hamstring ACL reconstruction.¹⁹ The inadvertent injury of the sensory nerve branches may occur during the skin incision, the dissection for the tendons, tendon stripping (as the saphenous nerve courses superficial to gracilis), and tibial tunnel drilling.¹⁹ However, it seems that the more distal the location of the area of disturbed sensitivity (as occurs after hamstring tendon harvesting), the less discomfort will result.⁴⁵ In contrast with patellar tendon harvesting, the area of sensory changes is more proximal and thus more bothersome.

Concomitant meniscal surgery during ACL reconstruction may result in range of motion problems during rehabilitation, which will influence the incidence of anterior knee problems.

Residual anterior instability after surgery can cause anterior knee problems secondary to the altered patellofemoral kinematics (lateral patellar tilt and shift) present in ACL deficient knees.

Proper placement of the drill holes at the isometric point is a prerequisite to achieve full range of motion postoperatively.⁴⁰ It has been found in a study that after BPTB ACL reconstruction, patients with patellofemoral joint arthritis tended to have more anterior placement of the femoral tunnel and more posterior placement of the tibial tunnel than those without patellofemoral joint arthritis.¹⁷

Arthrofibrosis after ACL reconstruction may result from an exaggerated inflammatory response, synovitis, or a sympathetic algodystrophy and will cause range-of-motion deficit.¹⁰

Formation of a “Cyclops” lesion is another reason for extension deficit and anterior knee pain.⁴⁶ This lesion is usually formed anterolaterally to the tibial tunnel placement of the graft. Arthroscopic débridement of the nodule can improve extension.

Anterior Knee Problems Related to Rehabilitation

An operation performed too early (i.e., before regaining full range of motion) is a well-known cause of postoperative range of motion deficit. For this reason we support a rather delayed reconstruction, not less than 2 months after the injury, to allow for posttraumatic synovitis to settle or the knee to regain full range of motion without effusion.^47,⁴⁸

Reduced strength and loss of range of motion are correlated with anterior knee pain after ACL reconstruction using all kinds of grafts.⁴⁹ Thereby every effort should be made postoperatively to achieve full range of motion and regain quadriceps and hamstrings muscle strength. Loss of hyperextension can be a significant cause of anterior knee discomfort after ACL reconstruction.⁵⁰^–⁵³ The reason for anterior knee symptoms in loss of extension is the resultant increase of patellofemoral joint reaction forces. It is not only loss of extension that can cause anterior knee symptoms but loss of flexion as well, although this has been more controversial.^52,⁵⁴ Patients with both flexion and extension deficits have more anterior knee pain than patients with an extension deficit alone.⁴⁰ The reason for anterior knee symptoms in loss of flexion is the decreased muscle strength in both flexor and extensor mechanisms⁴⁰ (Fig. 79-5).