Conservative Treatments for Patellar Tendinopathy: A Review of Recent High-Quality Evidence

: Patellar tendinopathy is a common injury characterized by progressive activity-related anterior knee pain. It is highly prevalent in sports which involve jumping and changing direction. The aim of this paper is to review recent high-quality evidence regarding the effectiveness of physical therapy in the treatment of patellar tendinopathy. Randomized controlled trials ( n = 22) researching the effects of exercise therapy, physical agents, and soft tissue techniques were included. The results show that exercise therapy is the most effective. While eccentric exercise is commonly used, very promising progressive tendon-loading exercise therapy programs are recently emerging. Extracorpo-real shock wave therapy, dry needling, and orthoses are no more effective than eccentric exercises or placebo groups. Isometric and isotonic exercise, patellar strap, sports tape, and kinesiotaping have a short-term effect on functional improvement and pain reduction, while progressive tendon-loading exercise


Introduction
While all tendons in the human body are subjected to injury and overuse [1], patellar tendinopathy (PT), also known as jumper's knee, is one of the most common lower limb tendinopathies [2].It is an overuse injury of the patellar tendon and reflects in anterior knee pain.Pain occurs at the proximal attachment of the patellar tendon at the patellar apex.PT is very common among active young individuals aged between 15 and 30 years, often among basketball, volleyball, and soccer players [3,4].In one study on elite athletes, point prevalence has been reported to be as high as 14.2% (87 of 613) [3].In adolescent athletes, PT is three times more common (5.8%) than Achilles tendinopathy (1.8%) [5].A recent study reported the prevalence ranging from 14 to 73% in different track and field athlete subgroups; however, the sample sizes were very small [6].In addition, PT is also prevalent in the general population, with 28.3% prevalence reported within a cohort of 50-79-year-old participants with no history of knee injury [7].
Jumping, landing, cutting, and pivoting require the patellar tendon to repeatedly store and release energy [3,8,9].Excessive repetitions of such activities or insufficient time between loadings lead to mechanical changes in the tendon, which appear to be a key driver for developing the symptoms [10][11][12][13].An important extrinsic factor is also a change in the type of playing surface, with symptoms occurring most often among athletes playing on hard surfaces [14,15].Van Der Worp et al. [16] reported that weight, body mass index, waistto-hip ratio, leg-length difference, the arch height of the foot, vertical jump performance, hamstring and quadriceps flexibility, and quadriceps strength are intrinsic risk factors for PT.Patella alta and larger infrapatellar fat pad are also risk factors in men [17,18].The incidence of PT is two to four times higher in boys and men compared to women due to the influence of estrogen [19,20].
Cook and Purdam [21] define the three stages continuum of tendon pathology.Increasing or decreasing load is the primary stimulus that defines the stage of the continuum.Reducing load may allow the tendon to return to a previous structural and capacity level within the continuum [10].The reactive stage is a non-inflammatory response of tenocytes and matrix due to acute overload or direct blow directly to the patellar tendon [21].The number of tenocytes and proteoglycans that bound water increases [22].The reactive stage is a short-term adaptation of the tendon to overload [21].If the overload is sufficiently reduced or if there is sufficient time between loading sessions, the tendon can revert to the normal stage.Clinically, it is observed as swelling and pain localized at the patellar tendon.Tendon dysrepair is an attempt at tendon healing.There is an increase in the number of cells, reulting in the increased production of proteoglycans.This causes separation of the collagen and matrix disorganization [21].Instead of collagen type I, disorganized collagen type III is produced [23].With load management, this stage is still reversible [24].In the degenerative stage, cell apoptosis occurs [25].Matrix and vascular changes are extensive, and due to that, there is little chance for reversibility of pathological changes [21].Individuals have recurrent bouts of pain that resolve and return with load management.Extensive degenerative tendon changes or high load can lead to tendon rupture [26].Around 97% of ruptured tendons already had previous degenerative changes [27].A reader interested in details of PT pathogenesis is directed to other papers [28].
PT is one of many pathologies that reflects anterior knee pain [29].Specific clinical features are pain localized to the inferior pole of the patella and load-related pain on the knee extensors [15,30].Tendon pain occurs immediately upon loading and stops when the load is removed, very rarely in the resting state [31].PT also has other symptoms, such as pain with prolonged sitting, squatting, and using stairs.These symptoms can also be present in other pathologies-patellofemoral pain, Osgood-Schlatter syndrome, infrapatellar fat pad syndrome, plica, infrapatellar bursitis, or Sinding-Larsen-Johansson syndrome [17,29,[32][33][34].
A basic check-up requires a thorough examination of the lower limb to identify any potential deficits in the hip, knee, ankle, and foot [15].These deficits affect the coordinated movement of the lower limb kinetic chain and prevent the optimal development of muscle strength and load bearing [30].Reduced strength in the gluteus maximus, quadriceps, and calf is often present in PT [30,35].It is important to quantify the patient's level of dysfunction and pain.VISA-P score (the Victorian institute of sport assessment-patella) is a 100-point scale that assesses symptoms, simple tests of function, and the ability for sports activities [36].Diagnostic imaging does not confirm PT, as pathological tendon changes may be present in asymptomatic individuals [12].Symptoms often improve without corresponding structural changes on magnetic resonance or ultrasound imaging [37].
Although there is a wide range of techniques for the treatment of PT, a review of the literature reveals the inconsistency of physical therapy.Furthermore, the authors are not unanimous about the effectiveness of the individual method and the combination of several techniques.The aim of this review is to collect and analyze the latest evidence on the effectiveness of physical therapy for the treatment of PT.Studies about exercise therapy, physical agents, and soft tissue techniques were included.

Materials and Methods
A systematic search was performed in March 2022 in the PubMed database and the reference lists of relevant reviews as well as the papers already included during the process.We also performed a search in Google Scholar and ResearchGate databases.Randomized controlled trials from the last twelve years were included.The database was searched with the following combination of search keywords: (patellar tendinopathy) and (treatment OR rehabilitation).To define the research questions, the PICOS strategy was used, as shown in Table 1.Studies comparing medical and surgical treatments and studies on pathologies other than PT were excluded.

Results
After screening 415 hits in the PubMed database and the examination of the reference lists of the included articles and the available systematic reviews, 62 studies were initially included.After the abstract examination, we excluded 22 studies, and after the full-text examination, we excluded three studies.Two more studies were included after reviewing the reference lists of relevant reviews.From the final pool of included studies, 14 studies were used to compare the effectiveness of physical therapy.Seven studies investigated the efficacy of exercise therapy (isometric, isotonic, progressive exercise), five physical agents (extracorporeal shock wave therapy), two soft tissue techniques (dry needling), two orthoses, and other related interventions (kinesiotaping, patellar strap, sports tape), and two platelet-rich plasma.A summary of the characteristics of the selected studies is available in Table 2.In both cases, the pain score was immediately lower post-exercise for an average 0.9 (p = 0.028).There were no significant differences in pain reduction between 45 min post-exercise and baseline (p = 0.089).There was also no difference between isometric and dynamic exercise interventions immediately after the exercise (p = 0.73) or 45  There was a pain reduction after 4 weeks with isometric exercises from average 6.3 to 4.0 (p = 0.003) and isotonic exercises from 5.5 to 2.0 (p = 0.012).VISA-P score also improved with isometric exercises from average 66.5 to 75.0 (p = 0.003) and isotonic from 69.5 to 79.0 (p = 0.028).There was no significant difference in pain (p = 0.208) and VISA-P (p = 0.965) score change between groups Both isometric and isotonic exercise programs can reduce pain and improve function during the sports season DN and PRP are both effective in accelerating the treatment of PT.While the latter appears to have a better short-term effect, after 26 weeks, there were no major differences between the treatments.The study included 2-, 6-, and 12-month follow-ups.PRP group received 2 autologous PRP injections (6-7 mL) over 2 weeks (1 injection per week for 2 weeks) under ultrasound guidance.ESWT group received three sessions, wherein 2.400 impulses were administered with an energy flux density of 0.17 to 0.25 mJ/mm VISA-P score was similar in both groups at baseline and after two months but showed larger improvements for PRP after 6 and 12 months (p = 0.014-0.026).The same pattern was observed for VAS, as PRP injection group showed better results than ESWT group at 6-month (mean 2.4 vs. 3.9; p = 0.028) and 12-month (mean 1.5 vs 3.2; p = 0.009).PRP also showed better treatment success and satisfaction at 12-month follow-up Both PRP injections and ESWT are effective treatments for athletes with PT.While they show comparable effects in the short term, the PRP group improved more at 6 and 12 months of follow-up Legend: MVC = maximum voluntary contraction; VAS = visual analogue scale; SLDS = single-leg decline squat; US = ultrasound; ROM = range of motion; RM = repetition maximum; ESWT = extracorporeal shock wave therapy; VISA-P = the victorian institute of sport assessment-patella; PT = patellar tendinopathy; NRS = numeric rating scale; KT = kinesio tape; EE = eccentric exercise; HSR = heavy slow resistance (90% of 1 RM); MSR = moderate slow resistance (55% of 1 RM), PTLE = progressive tendon loading exercise; DN = dry needling; PRP = platelet-rich plasma.

Discussion
PT is a common lower limb tendinopathy, but despite a wide range of methods, there is no consensus regarding physical therapy.The aim of this review was to investigate and compare the effectiveness of exercise therapy, physical agents, platelet-rich plasma (PRP), and soft tissue techniques for the treatment of PT.The results show that exercise therapy is the most effective, while other interventions may serve as useful and beneficial adjunct therapies.

Eccentric Exercise
Eccentric exercise involves active muscle lengthening and is characterized by a greater load compared to isometric and concentric exercises [54].Eccentric exercise improves the mechanical properties of the tendon and consequently increases its load-bearing capacity [21].van Ark et al. [43] found no tendon structural improvements with isometric and isotonic exercise after 4 weeks.Older studies suggest that the most effective exercise is the eccentric decline squat with the heels raised more than 15 • [55,56].Dimitrios et al. [2] found that eccentric exercise combined with static stretching of the quadriceps femoris and hamstring muscles at least 30 s before and after exercise had a greater pain reducing and function improving effect than eccentric exercise alone.Load management is one of the most important methods of treating PT.It affects matrix reorganization, collagen synthesis, reduced tenocyte activity, and reduced pain perception [57][58][59].Higher knee extension load improves muscle strength and nerve activation [60].Kongsgaard et al. [61] reported that heavy, slow resistance training from 15 to 6 repetition maximum (RM) affects the synthesis of new collagen networks and thus has a long-term impact on clinical improvement.In this systematic review, Agergaard et al. [41] found no difference between high (90% 1 RM) and moderate load magnitude (55% 1 RM) for the clinical outcome.

Other Exercise Types
Studies on isometric, isotonic, and progressive tendon-loading exercise therapy were also included.A significant progression was made in progressive tendon-loading exercise therapy, which improved the VISA-P score improved by 24 points [42].With progressive tendon-loading exercise therapy, the tendon gradually adapts to normal functioning [62].As described by Scott et al. [58], isometric exercise provides initial stimulation of the muscle and tendon, progressive loading adapts the tendon to the loads, and subsequent eccentric exercise is preparation for sport-specific activities [58].Rio et al. [44] reported that isometric exercises reduce pain in the early phase of rehabilitation.Isometric exercise with short-duration loads has been shown to be more effective as it is easier to tolerate [38].Holden et al. [39] reported that the analgesic effect is only seen 45 min after exercise.van Ark et al. [40].Holden et al. [39] found an equivalent short-term analgesic effect of isometric and isotonic exercise.
In addition to exercise therapy, passive interventions are also used in the treatment of PT, although evidence of their effectiveness is limited [15].Malliaras et al. [29] contend that the treatment of PT should focus on progressively developing load tolerance of the tendon with exercise and that other modalities are only beneficial as an adjunct to exercise therapy.Rutland et al. [63] agreed and stated that active rest, activity modification, and eccentric exercise are cornerstones of PT management.

Extracorporeal-Shock Wave Therapy
ESWT is based on mechanical shockwaves that travel through the affected tissue [64].A shockwave is a special, non-linear type of pressure wave characterized by a short rise time (10 us) [65].According to Zwerver et al. [48], ESWT is not effective as a solitary treatment during the competitive season.Although ESWT improves clinical outcomes, it is not more effective than eccentric exercise alone [45,46,66].van der Worp et al. [45] found no difference in effectiveness between focused and radial shockwave therapy.Notable improvements in VISA-P scores were achieved in the study by Lee et al. [47] with low-intensity ESWT once a week in combination with EE.Vetrano et al. [53] showed that three sessions of ESWT were effective in facilitating long-term PT treatment; however, PRP injections were even more effective.Despite a relatively small body of evidence, ESWT is a commonly used intervention for the treatment of tendinopathies in the lower and upper extremities [66-68].

Platelet-Rich Plasma Injections
PRP is a concentrate of platelets and growth factors obtained by centrifugation from a sample of patient's blood sample [69] and is believed to enhance the tissue healing process.Indeed, increased levels of macrophages and type I and III collagen in tendons treated with PRP have been shown [70].However, only two studies involving PRP application were included in this review [52,53].Dragoo et al. [52] found that PRP was more effective for accelerating the treatment of PT than dry needling in the short-term (12 weeks) but not long-term follow-up (26 weeks).In addition, Vetrano et al. [53] reported that PRP injection had a similar effect to ESWT therapy in the short term; however, at one-year follow-up, PRP appeared superior.The superiority of PRP over ESWT was also noted in a recent review [71].While further high-quality studies are needed, PRP appears as an effective approach to accelerate PT treatment.

Soft Tissue Techniques
López-Royo et al. [51] also found no significant effect of dry needling compared to EE.On the contrary, dry needling accelerated the improvement of PT symptoms in individuals that did not respond to exercise alone within 6 weeks.Other commonly used soft tissue techniques are fascial manipulation and transverse friction massage [72].Chaves et al. [73] showed that deep friction massage induces an immediate reduction in pain intensity.Similar effects were demonstrated by Pedrelli et al. [74] using fascial manipulation of the quadriceps muscle.According to their report, manual pressure raises the temperature of the ground substance and allows it to be transformed from a pathologically dense to a physiologically fluid state.The change in density allows the restoration of gliding between the connective-tissue layers and allows the free intrafascial nerve endings to slide within the fascia more freely, which explains the sudden decrease in pain [74].

Other Treatment Modalities
Orthoses also have an effect on short-term pain reduction.Patellar straps and sports taping also tend to show some benefits.The infrapatellar strap prevents overloading of the patellar tendon at degenerative sites by increasing the angle between the patella and the patellar tendon and decreasing patellar tendon length [75].An additional study showed the potential of kinesiotaping to reduce pain associated with PT [49].
This systematic review shows that isometric and isotonic exercise, patellar strap, sports tape, and kinesiotaping have a short-term effect on functional improvement and pain reduction, while progressive tendon-loading exercise, PRP, dry needling, and extracorporeal shock wave therapy have potential long-term effects.As a limitation, only studies comparing the effectiveness of movement therapy and one passive method were included in this systematic review.The results show that eccentric is more effective than passive methods.A retrospective chart review by Vander Doelen and Scott [76] showed that a multimodal treatment approach of a combination of dry needling, ESWT, manual, and exercise therapy have short-and long-term effects on functional improvement and pain relief.Despite the positive effects of the combination of methods reported by Vander Doelen and Scott [76], there is no research in this systematic review to support this.The heterogeneity among the included studies is a strong limitation of this systematic review.Included physiotherapeutic methods have different outcome measures, so it was difficult to compare their effectiveness with each other.The studies also differ in terms of the duration of the method, the participants, and the conditions under which they were carried out.Some of the studies were carried out during the competition season, while some participants had to stop training and only do the prescribed therapeutic exercise.Despite the number of studies, there is still no consensus on the most effective method or rehabilitation protocol.Eccentric presents the most evidence of effectiveness, while other passive techniques still need further research.

Conclusions
The results of this review show that recent high-quality evidence supports exercise therapy as the most effective for treating PT, and novel progressive tendon-loading exercise therapy programs are appearing as an alternative to eccentric-exercise-only approaches.ESWT, dry needling, and orthoses are no more effective than eccentric exercises or the placebo group.Isometric and isotonic exercise, patellar strap, sports tape, and kinesiotaping have a short-term effect on functional improvement and pain reduction, while progressive tendon-loading exercise, dry needling, PRP, and extracorporeal shock wave therapy have long-term effects.Despite the number of studies, there is still no consensus regarding PT rehabilitation protocol or evidence of the effectiveness of the combination of different physical methods and techniques.

Table 1 .
PICOS criteria for inclusion and exclusion of studies.

Table 2 .
Characteristics of the selected studies.