Tendons are fibrous tissue structures originated in the muscle and which get inserted into the bone. Their function is very similar to the one of the ligaments, a fibrous cord connecting two bones.

The patellar tendon is located in the knee joint. It’s a continuation of the quadriceps muscle and it attaches the patella to the shinbone. It is one of the strongest tendons of the body: it is capable of sustaining a stress 8 times as much as the body weight. Thus, one of its main functions is to help us carry out activities such as walking, running, or jumping.

Patellar tendinopathy

Patellar tendon overuse, compressive strength (in deep fascicles, in the interior muscles), stress or repetitive overload may cause pathologies such as the patellar tendinopathy, also known as “jumper’s knee” (read reference 1 below)(proximal tendon injury). This is very common in sports in which there are frequent jumps, changes of direction, accelerations and decelerations such as basketball, athletics, or handball. However, recent studies have demonstrated that patellar tendinopathy is a pathology that might be caused by many factors and which is not only aggravated when jumping (read ref.1).

The tendon’s ability to sustain workloads is individual in nature. However, there are common factors that increase the risk of developing a tendinopathy (read ref.2). The common risk factors can be classified in extrinsic (acting on the body and related to the workload), and intrinsic (biomechanical factors, acting from within the body).

Normally, the mechanical characteristics of the tendon improve whenever it gets an optimal workload that enables tissue recovery (read ref. 3). However, when there is an excessive load, the recovery process cannot be completed, the load is not sustained, and, consequently, the tendinopathy arises: there are changes in the tendon structure causing a collagen fibres misalignment, and the loss in continuity leads to a degeneration of the tendon. Such degeneration can be symptomatic (localized pain in the tendon as well as decreased activity and sports performance -read ref. 4, 5-) or asymptomatic (ref. 5) (painless changes in the structure of the tendon).

Patellar tendinopathy in sports

Patellar tendinopathy is one of the most frequent pathologies in professional athletes: some studies reported that 44.6% of volleyball players and 31.9% of basketball ones suffer from it6. When considering handball, the patellar tendinopathy incidence in professional players is higher than in younger players, but lower in basketball, volleyball, and roller hockey players (read ref. 6, 7).

Even though there is evidence that the tendon gets adapted to the training load, the structural changes in the patellar tendon in response to the training loads are not yet clear. To help investigate this aspect, Ortega-Cebrián, S. et al. carried out the study Patellar Tendon Structural Adaptations Occur during Pre-Season and First Competitive Cycle in Male Professional Handball Players (2021), which is summarised here. Its aim is to identify patellar tendon structural changes during the pre-season and the first competitive cycle in a group of handball players. 

Patellar tendon and handball

In handball, physical skills such as strength, power, endurance, velocity, agility, and coordination are required at high intensity (read ref. 7, 8). These excessive storage and release energy mechanisms increase the risk of developing patellar tendinopathy due to the forces received by the tendon (read ref. 7, 9). 

When the tendon is subject to great demands, it is believed that possible alterations in tendon structure could impact athletic performance. If the tendon structure tends to lose mechanical transducers in the tendon matrix, then decreased accumulation of energy storage and alteration of the stretch and shortening cycle will occur (read ref. 10).  Hence, it may be assumed that jumping performance could be affected by changes in tendon structure.

Among all knee injuries in professional handball players, patellar tendinopathy has a poor prognosis, occurring generally during pre-season and after the first competitive cycle and being associated with increased training and competition load (read ref. 8, 9). 

Quantifying how and when the patellar tendon adapts to training loads during this period of time could provide better understanding of the onset of patellar tendinopathy.

Characteristics of the Study

To carry out this study, a group of nineteen male professional handball players was formed.  Only 13 of them completed the data collection process due to injuries and time out of training. The result was the following group: age = 20.1 ± 2.5 years old; height = 179.2 ± 3.36 cm; weight = 81.32 ± 6.9 kg.  

In order to identify the state of the tendon, UTC scans of patellar tendon and the jumping performance test (CMJ) were performed. To carry out the comparisons, measures were taken on the first day and last day of pre-season training and at the end of the first competitive cycle.

UTC (Ultrasound Tissue Characterization) is an imaging technique specially designed for tendons. By means of a colour scale, it’s possible to determine the degree of the tendinous tissue alteration and minor changes in the tendinous fibre alignment can also be measured.

This classification of echo types based on colours allows monitoring of tendon integrity during treatment and collagen adaptation to load during a certain period of time, as well as identifying potential pathology in asymptomatic subjects (read ref. 11). 

The Counter Movement Jump (CMJ) is performed from a standing position with hands placed on hips. Then, a knee flexion is performed (reaching a 90-degree angle) followed by a quick jump extending legs. The variable was the power of the jump measured with a force platform.

Main Conclusions of the Study

After tracking players during this period of time, the following conclusion could be drawn from the study: 

– Patellar tendon structural changes were observed mainly during pre-season training and throughout the first competitive cycle. 

– Changes occurred in all portions of the patellar tendon, although proximal and distal tendon showed greater change than mid tendon throughout the pre-season and first competitive cycle. 

– Although changes in tendon structure were seen at the end of the first competitive cycle, a mild decrease in healthy tendon and increase in injured tendon was seen. 

– An association was found between tendon structural changes and jumping performance in the proximal tendon of the dominant leg. 

It was concluded that the patellar tendon shows greater structural change after completing pre-season training than at the end of the first competitive cycle, from which it may be inferred that excessive loading during pre-season training does not allow the tendon to adapt and potentially increases the onset of patellar tendinopathies. However, there is a need for further investigation to, for instance, quantify the amount of disorganised tendon that is needed to reduce performance or become asymptomatic.

References:

1. Lian, Ø.; Engebretsen, L.; Bahr, R. Prevalence of Jumper’s Knee Among Elite Athletes from Different Sports a Cross-Sectional Study. Am. J. Sports Med. 2005, 33, 561–567. [CrossRef]

2. Rudavsky, A.; Cook, J.; Docking, S. Quantifying Proximal Patellar Tendon Changes during Adolescence in Elite Ballet Dancers, a 2-Year Study. Scand. J. Med. Sci. Sports 2018, 28, 2369- 2374. [CrossRef]

3. Magnusson, S.; Langberg, H.; Kjaer, M. The Pathogenesis of Tendinopathy: Balancing the Response to Loading. Nat. Rev. Rheumatol. 2010, 6, 262–268. [CrossRef] [PubMed]

4. Lundgreen, K.; Lian, O.B.; Engebretsen, L.; Scott, A. Tenocyte Apoptosis in the Torn Rotator Cuff: A Primary or Secondary Pathological Event? Br. J. Sports Med. 2011, 45, 1035–1039. [CrossRef]

5. Cook, J.; Rio, E.; Purdam, C.R.; Girdwood, M.; Ortega-Cebrian, S.; Docking, S.I. El Continuum de La Patología de Tendón: Concepto Actual e Implicaciones Clínicas. Apunt. Med. Esport 2017, 52, 61- 69. [CrossRef]

6. Florit, D.; Pedret, C.; Casals, M.; Malliaras, P.; Sugimoto, D.; Rodas, G. Incidence of Tendinopathy in Team Sports in a Multidisci- plinary Sports Club Over 8 Seasons. J. Sports Sci. Med. 2019, 18, 780–788.

7. Monaco, M.; Rincón, J.; Montoro-Ronsano, J.B.; Til Perez, L.; Drobnic, F.; Vilardaga, J.; Puigdellivol, J.; Pedret, C.; Rodas, G. Epidemiología Lesional Del Balonmano de Elite: Estudio Retrospectivo En Equipos Profesional y Formativo de Un Mismo Club. Apunt. Med. Esport 2013, 49, 11- 19. [CrossRef]

8. Póvoas, S.; Seabra, A.; Ascensão, A.; Magalhães, J.; Soares, J.; Rebelo, A. Physical and Physiological Demands of Elite Team Handball. J. Strength Cond. Res. 2012, 26, 3365–3375. [CrossRef]

9. Monaco, M.; Rincón, J.; Montoro-Ronsano, J.B.; Drobnic, F.; Til Perez, L.; Toda, L.; Pedret, C.; Vilardaga, J.; Rodas, G. Estudio Prospectivo de Maduración, Desarrollo e Incidencia Lesional En Balonmano Formativo de Élite. ¿Puede El Estado Madurativo Ser Un Factor Determinante de La Incidencia Lesional En Balonmano? Apunt. Med. Esport 2014, 50, 5- 14. [CrossRef] 

10. Khan, K.; Scott, A. Mechanotherapy: How Physical Therapists’ Prescription of Exercise Promotes Tissue Repair. Br. J. Sport. Med. 2009, 43, 247–252. [CrossRef]

11. Van Schie, H.; Docking, S.; Daffy, J.; Praet, S.; Rosengarten, S.; Cook, J.L. Ultrasound Tissue Characterization, an Innovative Technique for Injury-Prevention and Monitoring of Tendinopathy. Br. J. Sports Med. 2013, 47, e2. [CrossRef]