Injuries of the Patellar Tendon

Pathological Conditions of the Patellar Tendon

Acute Tears of the Patellar Tendon


The patellar tendon is part of the extensor mechanism of the knee that includes the quadriceps muscle, quadriceps tendon, patella, patellar tendon and tibial tubercle (TT). The patella is considered the largest sesamoid bone of the body. For this reason, the patellar tendon may be considered a ligament because both its origin and insertion are on bone tissue (patella and TT). Its mean length is 50 mm, and it has a mean width of 30 mm. The distal insertion is slightly narrower than that at the patellar attachment.


The extensor mechanism can be injured in different locations. A fracture of the patella is the most common location. It is followed by quadriceps tendon ruptures and finally patellar tendon tears. Patellar tendon ruptures show a peak at around age 40 and represent around 0.6% of tendinous injuries in the general population. Although patellar fractures are more common in women, patellar and quadriceps tendon ruptures are more common in men. Hormonal changes during the menstrual cycle or greater laxity might help protect women from these injuries.

Risk Factors

Most ruptures are reportedly related to chronic lesions of the tendon. Patellar tendinosis leads to a weaker tendon, which has a greater risk of rupture. There are different conditions that predispose to patellar tendon ruptures, such as repetitive local steroid injections and metabolic diseases (systemic lupus erythematosus, rheumatoid arthritis, diabetes mellitus, renal insufficiency or other connective tissue diseases) that produce a microscopic alteration of the blood supply and subsequently a degeneration of the tendon. The aetiology of chronic tendinosis is often unclear, and it has been attributed to repeated tendon microtrauma, which is characteristic of jumper’s knee. This is often observed in different sports like basketball, volleyball or running.

Rupture Mechanism

Most patellar fractures are due to a direct trauma to the knee. However, patellar or quadriceps tendon ruptures are typically produced by an indirect mechanism. They occur as a result of eccentric contraction of the quadriceps muscle against a strong apposition with the knee partially flexed. When the knee is flexed more than 50 to 60 degrees, the patellar tendon supports a great amount of force. It is for this reason that most patellar tendon ruptures occur with the knee flexed. Different activities, like landing from a jump, stopping for a change of direction or running while climbing stairs are considered to be at-risk activities for rupturing the tendon in predisposed individuals.


Patients may describe an audible ‘pop’ or a sensation of their knee giving way during a movement with a sudden contraction of the quadriceps muscle with the knee in a flexed position. These patients have a palpable defect below the patella. They also present with an acute onset of pain and swelling on the anterior part of the knee after the trauma. A large ecchymosis and hemarthrosis are common around this area.

These patients are usually not able to maintain the leg in extension because of lack of continuity of the extensor mechanism. Sometimes patients can maintain active extension if the retinaculum is intact, but there is an evident extension lag. When the affected area is explored, a gap in the infrapatellar fat might be present.

Radiographic evaluation that includes two projections (anteroposterior and lateral view of both knees) should be performed. A proximally displaced patella, compared with the contralateral knee, can be visualised in the lateral view with a patellar tendon rupture. The Catton-Deschamps, Insall-Salvati or Blackburne-Peel indexes can be used to compare the patellar height with the contralateral knee. It is also important to rule out bone avulsions of the inferior pole of the patella or an avulsion of the TT in the radiological study.

Ultrasonography (US) can better confirm the diagnosis. With US it is possible to localise the exact location of the rupture. However, the use of magnetic resonance imaging (MRI) allows for a more precise diagnosis of the tear, including the location of the tendon rupture, and also to distinguish between partial and complete injuries as well as assessing the integrity of the retinaculum. In addition, MRI allows for diagnosing concomitant intraarticular injuries. In conclusion, MRI is the preferable imaging study to completely examine the knee after extensor mechanism injuries.


Nonsurgical treatment is only followed in partial tears of the patellar tendon without an extension lag and when the patient can keep the leg straight passively. The level of activity is also important in determining the best treatment alternative in partial tears. Although this can be well tolerated in less active patients, surgical treatment is preferable in patients involved in demanding sport activities or with a higher functional level. Patients with medical comorbidities contraindicating surgery can also be considered for conservative management. In these cases the leg should be maintained in full extension with progressive weightbearing. For these partial tears, progressive range of motion (ROM) can be initiated around the third to sixth week, depending on the amount of tendon torn.

Surgical repair should be indicated for all complete tears or partial tears with functional dysfunction in active patients. The type of surgery will depend mostly on the height of the patellar tendon disruption.

Proximal Avulsion

Detachments of the patellar tendon at the inferior pole of the patella ( Fig. 33.1 ) should be reinserted into its native attachment. For this the most common technique involves drilling three vertically oriented 2- to 3-mm holes in the patella. Posteriorly, two or three Krakow sutures with nonabsorbable braided polyblend sutures should be performed as indicated in Fig. 33.2 . Finally, the suture ends (four to six) should exit the proximal border of the tendon. The sutures are then introduced through the drilled patellar tunnels. For this, any type of suture shuttling device, such as a Hewson passer or Kirschner wire (K-wire) with an eyelet, can be used. Then the sutures’ ends are tied between them with sutures exiting from other patellar tunnels as a bridge ( Fig. 33.3 ) at 30 degrees or more of knee flexion.

Fig. 33.1

Proximal patellar tendon rupture in a right knee.

Fig. 33.2

Proximal avulsion of the patellar tendon at its insertion site in a right knee.

(A) A suture passer is being used. (B) The passing sutures (dark sutures) and the Krakow sutures along the patellar tendon are seen. (C) The passing sutures are about to be pulled proximally to retrieve the suture ends exiting the patellar tendon. (D) Final aspect of the patellar tendon reattachment.

Fig. 33.3

Transosseous reattachment of a proximal patellar tendon rupture to the patella in a right knee.

It is crucial to check the patellar height before the sutures are tied down. For this an intraoperative fluoroscopic evaluation comparing it with the contralateral knee is recommended. In case it is not possible to evaluate the contralateral knee with it at 45 degrees of flexion, the inferior pole of the patella might be right above the intercondylar notch.

The use of a backup protection technique to protect the tendon repair is also recommended. This allows the patient to initiate the ROM immediately after the surgery. Different techniques have been described. These are classically fixed between 60 and 90 degrees of knee flexion. Classically a horizontal hole is reamed across the TT. An 18-gauge wire is passed through this hole and posteriorly passed through the middle of the quadriceps tendon proximal to the patella. It is important not to iatrogenically create patella baja with this surgical step. This backup protection can also be done with any type of nonabsorbable braided polyblend suture or with a 5-mm Mersilene tape (or other type of synthetic tape) following the same technique.

Another option for proximal patellar tendon rupture repair is the use of anchors. Two to three anchors fixed in the distal pole of the patella can be placed with four to six sutures that are used to create a Krakow suture technique (or similar) to finally approximate the proximal aspect of the tendon to its native insertion ( Fig. 33.4 ).

Fig. 33.4

Repair of a proximal patellar tendon rupture with two bone anchors in a right knee.

Midsubstance Tear

At this point it is important to differentiate ruptures produced in a good- or poor-quality tendons. When good-quality tissue is present, it is possible to perform an end-to-end suture with a Krakow technique or similar. It is important to maintain the patellar height, as indicated in the previous section. This primary repair can be augmented with different systems, such as wire cerclage, nonabsorbable sutures, autogenous graft or tape. , An example of this repair is shown in Fig. 33.5 .

Fig. 33.5

The repair/reconstruction of patellar tendons injuries are better protected with cerclages made of wire, sutures, tape or tendon grafts that tighten at 60 to 90 degrees of knee flexion in a right knee. In this case a wire (arrows) was used.

However, if the tissue quality is not optimal or if it is a chronic injury, most authors recommend performing a reconstruction with an autograft. Because primary repair of chronic patellar tendon injuries provides the lower functional outcomes, augmentation with a graft is highly recommended in all these cases. Allografts and xenografts are also a valid alternative. The reported outcomes with any of the several described surgical techniques and with any graft source are comparable. Then it depends mostly on the surgeon’s preference.

Distal Avulsion

Distal avulsion is a very uncommon situation in adult patients. In fact, most studies reporting these injuries are case reports. Any type of anchor at the TT is usually used to restore the native tibial insertion in a similar fashion as described earlier for proximal tears.


Rehabilitation after a patellar tendon repair depends on the tissue quality, time from injury to surgery, age, need for augmentation and other conditions. In general, if the repair is strong and the tissue quality is reasonably good, the progressive increment of passive ROM immediately after the surgery can be started. These patients are also allowed to bear weight with the use of a brace fixed in full extension from the first postoperative day.

Functional Outcomes

Gilmore et al. reviewed different surgical techniques and reported that direct repairs without augmentation obtained flexion of 102 degrees and had a rerupture rate of 5%. In those patients with a direct suture protected by any type of wire or suture who initiated ROM early, a mean flexion of 129 degrees was reached and the rerupture rate was only 2%.

Patellar Ruptures and Total Knee Arthroplasty

Extensor mechanism disruption after a total knee arthroplasty (TKA) is a devastating complication. There is no consensus on the treatment algorithm in these cases. In general, direct repairs have higher complication rates than reconstructions. In 2019 Vajapey et al. published a review assessing the different series published on this issue. They concluded that both repair and reconstruction failure rates were high for all the described techniques. Achilles tendon allograft reconstruction has been considered the gold standard for late patellar tendon reconstruction. Other techniques involving the medial gastrocnemius flap have also shown promising results in these cases.

Patellar Tendinopathy


Patellar tendinopathy is a common cause of clinical consultation for both elite and recreational athletes. Although it has always been a prevalent condition, the scientific interest in the different therapeutic methods used has increased.

Patellar tendinopathy is identified as the cause of anterior knee pain as a result of small or large lesions of the connective tissue that makes up the tendon. The pain is usually more acute in the proximal part of the tendon. Because the tendon injury usually occurs in activities or sports that require jumping (such as volleyball or basketball), it is known as jumper’s knee .

The repetitive use or overuse of the knee extensor apparatus produces tissue stress that can cause tendon injury. , The proximal and deep portion of the patellar tendon, at its insertion in the patella, is the main area of injury. A patellar tendon lesion may be found at the distal insertion of the tendon (in the anterior tuberosity of the tibia) and more rarely in the middle area of the tendon.

Patellar tendinopathy mostly occurs in men between the second and fourth decades of life with accompanying intrinsic and extrinsic factors that lead to its appearance. The main extrinsic factor is overuse with jumps, braking and high loads. These cause a progressive deterioration of the collagen tendon fibres with microscopic changes that can end up causing tears in the tendon. Excessive frequency in training, the hardness of the surface where sports are carried out and the use of improper equipment are other causes of patellar tendon injury. The most important intrinsic causes are ligamentous laxity, patella alta, quadriceps muscle weakness, hamstring stiffness and knee malalignment. ,


The clinical diagnosis is made with a detailed physical examination. The patient generally has muscular weakness in the gluteus maximus, quadriceps and the gastrocnemius muscles, as well as a posterior leg chain elasticity deficit.

The patient usually refers to a pain located at the inferior pole of the patella in the insertion area of the patellar tendon. Symptoms increases when the patient performs squats, climbs stairs or sits for long periods. When strength training involving the knee occurs, the pain usually appears acutely, improving when the activity stops even though residual pain may remain for a couple of days.

The severity of patellar tendinopathy can be objectified with the Victorian Institute of Sports Assessment – Patella (VISA-P) questionnaire. This questionnaire focuses on pain, function and activity. The maximum score that can be obtained is 100 points (asymptomatic person = 100). The VISA-P can be used to assess the severity of symptoms and to monitor the results. ,

Patellar tendinosis can also be classified in the following categories:

  • grade 0: absence of painful symptoms

  • grade I: nonspecific pain without physical activity limitation

  • grade II: moderate pain during sport without performance limitation

  • grade III: pain with initial performance limitation

  • grade IV: pain with significant limitation in sports performance

  • grade V: pain in everyday life with inability to practice sport

Patellar tendon tears can be classified as:

  • intratendinous tears

  • partial tears

  • complete tears

  • complete tears with associated lesions (multiligament, meniscal lesions)

For the evaluation by means of imaging, the use of ultrasound or MRI is widely accepted. Ultrasound is a noninvasive, safe, reproducible and accurate technique that provides a high-definition image of the patellar tendon and adjacent structures. At the same time it provides a dynamic image that will help in understanding the patient’s injury.

US of patellar tendinopathy demonstrates a thickened tendon with loss of normal echogenicity (hypoechogenic tendon), intratendinous calcifications and erosions that are mainly located at the lower pole of the patella ( Fig. 33.6 ). , The use of colour Doppler imaging allows for visualisation of neovascularisation in proximity to the Hoffa fat pad. In more advanced injuries, if the injury mechanism persists, tears within the tendon can be found. They are also localised close to the lower pole of the patella, but in this case in the deepest or articular area of the tendon ( Fig. 33.7 ). They usually need a modern US system to be detected, showing an anechogenic area in the referred zone.

Fig. 33.6

Patellar tendon injury, ultrasound view. High-definition ultrasound image with a 5- to 16-MHz linear probe in longitudinal section and panoramic vision. A long-standing patellar tendinosis with tendon thickening (double arrow), hypoechogenic areas (∗) and hypervascularization (arrow) is seen.

May 3, 2021 | Posted by in ORTHOPEDIC | Comments Off on Injuries of the Patellar Tendon
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