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Chung compared clinical outcomes after tendon grafts and tendon transfers, finding no difference in
[84]
functional results between the procedures [Table 2].
Minami et al. reported good functional results using tendon graft after 1987, before which they had poor
[107]
results caused by flexion deficit after end-to-side repair with an adjacent tendon . In contrast, Nakamura
and Katsuki suggested that tendon grafting is unsatisfactory because finger flexion may be restricted as a
[76]
consequence of irreversible muscle contracture.

Tendon transfer is the most common surgical treatment for extensor tendon rupture. Shannon and
[103]
Barton suggested that the outcome of tendon transfer for finger extensor tendon ruptures is often poor.
Moore et al. reported that patients with a single extensor tendon rupture have good results after tendon
transfer, but that tendon transfer for three or more ruptured tendons associated with MP arthritis often
[106]
requires salvage procedures .
The duration of the untreated rupture is often long because rheumatoid patients are accustomed to
[108]
performing daily activities with a deformed hand (Nalebuff, 1987) . If joint destruction is apparent in the
MP joint or if multiple fingers are involved, the clinical result is poor and inversely proportional to the
duration of an untreated tendon rupture (Moore et al., 1987; Shannon and Barton, 1976) [103,106] . The patient
had a better outcome when one or two fingers were involved than when three fingers were involved, and the
[76]
duration of untreated rupture was related to the MP joint extension lag. Nakamura and Katsuki suggested
that the pulp-to-palm distance (a clinical outcome) and patient satisfaction (measured on the visual analog
scale) are related but that the MP joint extension lag and the patient satisfaction are not related.

REGENERATIVE SURGERY APPROACH TO TENDON DEFECTS
Regenerative medicine is a branch of translational research based on the clinical application of cell therapy,
promoting and stimulating the body's own repair mechanisms to achieve healing with complete
morphological and functional recovery in the absence of scar tissue. Regenerative Surgery (RS) defines all
the Regenerative Medicine treatments that can be clinically applied through minimally invasive surgical
procedures.

The three pillars on which Regenerative Medicine is based and acts are the interaction and integration of
'stem' cells, growth factors and scaffolds. When tissues get damaged, the most common body repairing
response is represented by scarring activity, which produces nonfunctional tissue. To be more precise, the
scar tissue possesses inferior mechanical and biochemical properties compared to native tissue , and this
[109]
is particularly true for tendon healing. In fact, the tendon, due to its low cellularity and poor blood supply,
has limited healing capacity; therefore, it is difficult to regain the original structure and function of the
tendon after damage. This is also due to the fact that tendon healing, which is composed of the three
classical phases of healing, namely the inflammatory phase, the proliferative phase and the remodeling
phase, is extruded through two distinct processes, which are intrinsic and extrinsic healing [110,111] . The
inflammatory phase is characterized by increased vascular permeability and the arrival of inflammatory cells
such as neutrophils, macrophages, T-cells, and mast cells. It is well known how abnormal macrophage
activity can cause fibrosis, and it has been shown that in macrophage-deprived tendons, there is decreased
scar production attributed to lower levels of cytokine transforming growth factor (TGF)-β. In contrast, the
proliferative phase is characterized by different fibroblast populations with mainly type III collagen
production. In animal models, the healing process starts at the epitenon, and the cells move from the
epitenon/paratenon into the injury area. The remodeling phase involves the transformation of granulation
tissue into scar tissue with a reduction in vascularity and cellularity. Unlike other tissues, however, tendons